The micro-pig, called Frances Bacon, lives at the Conquering Hero in West Norwood but started "minesweeping".
Customers also started letting her drink beer and cider.
Landlords Ian and Vicky Taylor-Ross said they only realised the Vietnamese Pot-Belly was drinking alcohol when she started butting into customer's legs.
Regulars to the pub have now been warned not to give her any beer and her owners are making sure she does not drink from glasses left by drinkers.
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Ian, 43, and Vicky, 39, have owned the four-year-old pig since she was six weeks old.
Frances, now fully grown, is becoming a bit of a "loveable menace", they said.
"She's lovely - definitely our favourite regular. We've had to bar her from having any beer though. "She managed to nick a pint or two and then started butting into people. But we're keeping a closer eye on her now and that won't happen again," Ian was quoted as saying by the BBC.
Frances will eat anything but has to be kept on a vegetarian diet at the pub and has her own space in the beer garden.
The parents believe the six-stone pig is a fantastic pet for their three children and the family regularly walk her on a lead.
She is also popular with their customers.
Vicky said: "Most of our punters really like her but it can be a bit weird for people especially as we are in London. She's just like a dog really, only craftier.