Yes I've lost my temper but only with a long time friend and long time FtF opponent who also loses his temper. It can get pretty heated and we remain friends (and still play) but I imagine it would look pretty funny to someone else.
Example: I don't quite remember what scenario we were playing but he (we'll call him 'D') had a couple of slow moving flame churchills moving along. I had both a little HIP for squads and some mines. So he slogged his churchills along with a squad to search. He came to a spot where he could search 4 hexes and he opted to search 4 potential (empty ground) mine hexes instead of the little woods hex I had my HIP squad with psk in. He pointed to each hex he wanted to search, waiting for my response and then pointed to the next one he wanted to search. I could tell he was thinking about searching the hex with my HIP squad in it but I think he figured that was too obvious since it was pretty far forward. He found nothing, in the next prep fire I killed his churchill with my HIP guy in the adjacent hex - the one he thought was too obvious, (with a snake eyes yet, not a critical hit but insulting all the same
), and that was it. The proverbial chit hit the fan.
D: 'I searched there!'
Me: 'No you didn't! You searched here, here, here and here!'
D: "Phfft! Whatever! How do you know which hex I searched?!'
Me: 'BECAUSE YOU FREAKING POINTED AT THEM AND SAID, "I SEARCH THIS HEX"!'
...and so on...
lol...oh man. It wasn't funny to us at the time but the arguments we get over based purely on a sense of competitiveness are hilarious.
We've been buds since the age of 17 so it's not like we couldn't get into an outright fist fight and not still remain friends but still, whew, we get into some tilts sometimes.
Other than that, no I don't really lose my temper. I have had a bout or two of sulking over bad dice rolls but that's rare.