Very rarely. Partly because I'm a somewhat non-competitive person (even when playing "competitive" games). I play for fun, and I have fun even when I lose, unless the winners are complete jerks about it. Partly because I lose fairly often (see above, not really a competitive person). The only time I really feel bad is when the opposing team is losing (usually badly), and it's clear there are one or two good guys on their team that are trying to carry the team, even though they know they're going to lose anyways because the rest of their team is that bad (not because our team is "just that good").
