This is what occasionally happens: I think of a blog post, think far too long about it, eventually write some notes, tinker with it, it's never right, forget all about it… then a reputable publication, usually The Guardian, pinches the idea and publishes it (this ties in with my notion of great ideas lingering in the air, just waiting for the right person to pluck (God I love that word; it's not an onomatopoeia, but it should be) them from the ether).
Anyway, my Eureka moment regarding tipping occurred only fairly recently. It's fairly simple, even obvious, but goes like this: if you pay for something before, don't tip. If you pay for something after, tip. So: McDonald's (etc), Starbucks (etc), cinemas, buses, trains, shops – one pays before, and doesn't tip (one knows exactly what one is getting, presumably*). Cafes (proper ones), restaurants, hairdressers, taxis, hotels – one pays after, and should tip, depending on what the service has been like.
Any confusion lies in how much one should tip. 10% seems acceptable in most countries. I never used to tip much, until I spent time with a bunch of waiters and waitresses in New Orleans, who were badly paid and relied on tips for their living (and berated me for tipping less than 20%). It's easier to tip a lot in foreign countries; I usually have no concept of how much the money is worth and just drop a ton of shrapnel on the table and hope for the best.
I find I tip more or less depending on who I'm with. If I'm with old friends, I probably won't tip much; if I'm trying to impress someone, I'll probably tip more. Either way, I quite like tipping, it makes me feel generous and mature. Though I won't tip at all if the service has been atrocious.
Read The Guardian's Guide to tipping in restaurants (written by a waiter).
*In the old days one could pay for a tube fare at the end of a journey. A dead friend of a dead friend used to pay only according to what the journey had been like; it had usually been abysmal, so he only used to pay a few pence (in the days when a single fare was 10p).
Previously on Barnflakes:
Plucked from the ether
Proud to serve
The risible fall of M. Night Shyamalan