The only bar where this never happened was this one bar we visited more regularly than any other. We had sympathised a lot with the waiters there. One of my buddies, a Lankan working with a medical NGO, eventually sponsored one of the waiters, a very shy and extremely nice ex-cop, by helping him build his own house in some rural place. I also gave a few thousand rupees to another waiter there so that he could start his own pig business (ouch ouch, my poor karma probably got hammered in the process). Nota bene: he wasn't a Buddhist but a Catholic ... no respectable Buddhist would ever think about sending pigs to the slaughter for a living.
Anyhow, this kind of regularity was only obtained after a couple of years of going there. ps: for curious people, the bar was owned by some local mafia guy. A picture of the Boss shaking hands with Premadasa, a former hardline SL president with possible underground connections, who got bombed by the LTTE, was throning over the main room. The bar was "upmarket" when compared to the downstairs one. Downstairs, it was cats and dogs hanging around, chicken bones flung over tables, drunkards in sarongs singing and singing and singing, weird tasting moonshine for very cheap ... but upstairs, upstairs we had the air conditioning, and a TV playing non-stop Bollywood movies ... drinks were twice more expensive than downstairs, the windows had been painted all black which made the place very dark. Plastic plants, red curtains ... frankly not a very nice looking place ... but man what a great hangout. We'd order booze either in grams or centiliters. For example, in Sinhala: "machang, mata arakku siyak denna" ("dude, bring me 100 cl of arrack").
By the way, a message you often see written in huge letters in Lankan bars is: "SINGING IS PROHIBITED". It's kind of a tradition there ... one table starts singing a Baila, a sort of Portuguese-inherited rythm (as the name also suggests) a bit like rap in the sense that you make up the lyrics which are not meant to be lewd, obscene, and sarcastic, but which end up being just that in bars ... and you make the lyrics rhyme. Then you sing off with your buddies hitting a beat with the furniture, or with the cutlery. So when this singing suddently erupts at a table, other people applaud the lyrics, and then another table will reply with the next verse, and join in in the rythm. Soon enough, the whole place will be hitting an excellent rythm on objets around the bar, and singing really loud. You can imagine the level of noise and laughter.
ps: a baila extract (MP3 file) ... I don't know if this link will work for long though
pss: I guess I'm feeling a bit nostalgic about the place, and that's why I wrote this long bit of trivia