Random personality-changes, ugh. So annoying indeed.
I've had some of my characters slightly change their personality.
One of my characters started as a rebel. She wanted to take over the city and kill people. The people taught her that killing isn't the best way to go and that the leader of that place was doing a great job.
The only reason I would see to have your character do something completely different, that goes against their personality, would be that the way they showed themself wasn't really them.
Basically a spy. First he acts nice, and once he has the keys he will pillage the village.
Other than something like that it would be pretty stupid.
And let me say that I agree with both of you when you guys say that a character shouldn't be sad and mean when spawning between all kinds of nice people.
But then again, what if he or she spawns in the middle of a war between two blood-thirsty clans? Then can he/she still be nice? I'd say no.
Either join the "fun", be a coward and run or panic.
I guess that in this discussion there are all kinds of definitions of "Bad roleplaying" that's different for everyone.
Some might think that killing you just for your items is stupid and bad roleplayed, others might see it as a smart thing to do of that young man. (This is entirely OOC, considering the character died).
Allthough I still completely disagree with the psycho characters needing a reason. My character is sick in her head. No reason for that at all.
It just happens to be that she was spawned (or born, if you prefer saying it like that

) like that.