The 23-year-old was responding to a question about being made to wait on court for his opponent, Spaniard Fernando Verdasco.
Learning disability charity Mencap has now called for the world No.19 to apologise.
In a post-match conference, he was asked: “Tennis etiquette requires that both players arrive on court at the same time. You were kept waiting about eight minutes. Any idea why?”
Tomic replied: “Yeah, I did get to the court prior to him very early, and unfortunately I had to stand on court like a retard.”
Ciara Lawrence, who has a learning disability and is a campaigns support officer at Mencap, slammed the Australian’s language.
“I’d like the player to apologise and would encourage him to meet people with a learning disability so he can understand why the word is so damaging and offensive,” she said.
“Time and time again I hear this word used as if it has no effect. People clearly don’t understand how upsetting and offensive this is to people with a learning disability like me.
“It makes people with a learning disability seem not as people but as second-class citizens, and is no different to discriminating against someone who is gay or black.”
The latest controversy to hit Australia’s tennis camp came after Nick Kyrgios – who promises fans “a circus” when he takes on German wildcard Dustin Brown in a rescheduled clash on Friday – was fined $US2500 ($A3,380) for unsportsmanlike conduct in his opening match.
Kyrgios drew the equal-heaviest sanction of the tournament thus far after raising the ire of umpire Mohamed Lahyani during his four-set win over Radek Stepanek.
Kyrgios has history with Lahyani, who took the unusual measure of advising the 15th seed and Stepanek pre-match to “be careful with the language and try to keep the racquet in your hand”.
The Australian refused to answer questions about Lahyani’s warning in his post-match press conference, having earlier joked “we’re good … we’re not good, but …”
Kyrgios, though, did challenge the Swede when he was handed his code violation, while clearly believing he was being singled out by the official.
“What did I say?,” Kyrgios said repeatedly.
“So you’re telling me every single person that has said that in this chair has got a code violation?
“You are telling me that? In the history of tennis? Every single person? You tell me that. That’s rubbish.”
Kyrgios’s lively start to the championships followed a series of clashes with officialdom during his run to the fourth round last year.
Former Wimbledon champion Pat Cash has counselled against trying to rein in tennis’s wild child as he continues to push the limits at the All England Club.
Asked on BBC how to solve the Kyrgios problem, Cash agreed with nine-times women’s champion Martina Navratilova’s “good luck” response and said his fire was all part of the package.
“The bottom line is that Nick is Nick and he’s going to blow up – and that’s his personality,” Cash said.
“He’s unbelievably interesting. A mate of mine said to me ‘when that Kyrgios kid comes on, I can not turn the TV off’.
“One, (because) he’s super-talented. Two, because you just never know what’s going to happen.
“But he is an unbelievable talent.
“Can you rein it in? Can you say ‘calm down?’ I’m not sure if that’s a good thing or a bad thing.
“Obviously you can’t go around swearing and throwing racquets when there’s kids and all that sort of stuff.
“He’s trying, but I don’t think it’s really him. It’s a bit like Andy Murray; do you say ‘you’ve got to stop getting emotional or stop getting grumpy?’
“He’s just not that personality.”
Navratilova said she wouldn’t go messing too much with the coachless talent either, while John McEnroe believes the 21-year-old has “got an opportunity to be something spectacular” if he can just temper his on-court emotions.
“I don’t think you need to really change anything,” Navratilova said.
“You don’t really need to coach him. You just need to channel it in the right direction so he doesn’t beat himself.”
McEnroe has long been a huge fan of the two-time quarter-finalist.
“I really believe he can be the best player in the world,” the former world No.1 told BBC 5 Live Sport radio.
“If he gets his head together and figures out how.”
Despite the off-field furore, Tomic safely advanced to the second round at Wimbledon, but conceded he’d rather have slept on his tenuous match-winning lead after surviving a nerve-wracking one-set shootout.
Tomic overcame two more rain delays and Fernando Verdasco’s ferocious firepower to prevail 4-6 6-3 6-3 3-6 6-4 in a tense first-round battle continuing on from Tuesday.
The 19th seed joins fellow Australians Nick Kyrgios, John Millman, Daria Gavrilova and Samantha Stosur in the second round, but the bleak weather in London left Wimbledon debutant Matt Barton on tenterhooks for a second night running.
Barton was locked at two sets apiece and 3-all in the decider when his titanic first-round tussle with fellow qualifier Albano Olivetti was abandoned on Wednesday night.
Samantha Stosur didn’t even set foot on court, with the 14th seed’s second-round clash with former finalist Sabine Lisicki wiped entirely from the third-day schedule.
But Tomic made the startling confession that he would have preferred not to return to court after a second rain stoppage and instead gone to bed leading Verdasco 5-3 in the fifth set.
“I was leaning on hopefully playing tomorrow and then not having to play (my) second (match) if I had have won,” he said.
“Now I have to play tomorrow.”
Weather permitting, the 19th seed will return tonight to face Moldovan qualifier Radu Albot for a likely crack at 14th seed Roberto Bautista-Agut.
Despite the apparent inconvenience of having to play three straight days – and backing up for a full match – Tomic said he fancied his chances of pushing into round three.
“Whoever won this match had a big chance of going further into the draw, for sure,” he said.
“I’m pretty happy, probably with my results. (I’ve had) some of the best grasscourt results prior to Wimbledon. It’s pretty solid.”
Tomic resumed against Verdasco with the match on a knife edge at two sets each after anxiously waiting another hour after the scheduled restart before the covers were removed from court three at the All England Club.
He gained the decisive break in the sixth game, much to the delight of Australian Davis Cup captain Lleyton Hewitt, who bellowed a signature “come onnnnn” from Tomic’s courtside box in celebration.
Tomic had to hold his nerve and serve from love-40 down to consolidate for 5-3 after fighting off five break points, only for light drizzle to force the players off once more for another four hours.
He finally put Verdasco away after two hours and 45 minutes of on-court action, despite the one-time Australian Open semi-finalist firing down 28 aces to Tomic’s 11 and clubbing 69 winners to 51.
Tonight’s action will now feature five Australians with Barton resuming at 6-7 (7-9) 7-6 (7-5) 6-3 6-7 (5-7) 3-3 in his bid to land his maiden grand slam main-draw scalp.
John Millman also chases a spot in the last 32 against Benoit Paire, while, like Stosur, Daria Gavrilova has a tough second-round assignment in 19th-seeded Eastbourne winner Dominika Cibulkova.
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