oddly, for all this arguing, I usually tend to overtip because...why not? If you can make someone feel appreciated while they trudge through what's probably a dreary job of waiting tables or pouring a beer, then a few bucks doesn't really matter.
I tend to kinda absent mindedly tip taxi drivers and waiters with what sems to be fair and I often seem to be told off for being generous by my companions, so I have no issue with tipping. But people demanding a tip, demanding a tip of a certain amount, asking for a tip for just doing their job which previously was performed without any extra inducement are all things that rub me up the wrong way.
With the thing about more expensive food garnering a bigger tip although requiring no more work, one instance springs to mind. It was a few years back when the Evening Standard was giving out these vouchers that gave something like eighty percent discount on meals at high end restaurants - not including drinks or desserts etc So although it looked like a really good deal, unless you were disciplined the price kept up pretty quickly anyway. But we smart and avoided any of the expensive stuff. So the meal would have cos, say, a ton so after the discount it should have been around twenty quid, however, to our chagrin the bill was almost twice that. It turned out that they had added a service charge of fifteen percent on the UNdiscounted price. We had a big argument about that with them claiming that it was fair to 'suggest' a service charge based on the cost of the food rather than the price we paid for the meal. Whatever the rights and wrongs here I think it highlights the arbitrary nature of tipping based on the cost cos clearly the work they did didn't change. Anyway they refused to back down so in the end we asked whether we had to pay the service charge... and they grudgingly admitted that it was optional. So... well, I can't remember, but I hope we gave them nothing the cheeky gits.