The poll of 1,000 diners by Voucherbox.co.uk discovered that as well as tipping for good service, one-fifth of Brits 'tip big' if they find the waiting staff attractive.
According to the survey, top of the list was a 'nice smile' - with 23% tipping for this alone.
But just having an 'attractive figure or build' would result in 14% of customers increasing their tip - and 8% said they would only ever tip attractive staff and not unattractive staff.
A quarter even said they would return to the restaurant as well if they found the waiting staff attractive.
Additionally, a 'flirty manner' resulted in 16% tipping and 'nice eyes' saw 11% parting ways with their cash.
Even characteristics like 'nice hair' or 'smelling nice' saw 8% and 10% gratuity for waiting staff - but 40% wouldn't tip at all if there was a bad body odour.
Dirty fingernails and greasy hair also saw diners turned off from tipping with a quarter and a third not offering a gratuity for such offences - and nearly a third wouldn't tip if the staff were 'scruffy'.
One diner said: “As a rule I only tip for outstanding service but if the waiter happens to be gorgeous that definitely helps make the experience better.
“It’s only human to enjoy the attention of an attractive person and if they offer a beautiful smile as well then on an almost subconscious level I’m more likely to be generous.”
A spokesman for Voucherbox.co.uk, who commissioned the research, said: “Only a minority of Brits admitted to tipping more money if they found the waiter or waitress attractive.
“But at 20% that is still a significant number. Interestingly a nice smile was much more important than an attractive build or figure when it came to persuading diners to part with their hard earned cash.
“It seems if waiting staff want to maximize their tips all they need is to make sure they do the three S’s - shower, shampoo and smile.”