I swear Americans are fucking retarded with tipping in restaurants, every time I hear it mentioned it's something petty, either pity-party shit about wage disputes that aren't the customers' responsibility to fix, or some early-20s waitress who's obviously a miserable cunt in person bitching that they only got $5 of free money rather than an arbitrary percentage of the bill.
Over here we'll just leave you a couple' quid if the service is good or walk out if it's not, simple as.