Does TV count? Kwai Chang Caine from Kung Fu, all he does is mind his own business until local Yahoos mess with him.
Those who hadn’t heard of him before. The trope is there, even if the title already points “there’s going to be things making lots of noise”.
Not a movie, but this happens in the Avatar-Last Airbender series, most noticeably with a certain mad old man.
…and then there’s the eponymous Drunken Master, of course.
Y’know, if Caine really believed in peace, he would have learned that Americans [del]have[/del] had a tradition of testing people for weakness and cowardice, and that if he only made a show of standing up for himself fewer people would have messed with him. As it was, he practically baited bullies into harassing him.
Willow got pretty badass in Buffy.
NOT following a TVTropes link.
Do amnesiacs count? If so, The Long Kiss Goodnight is pretty awesome on that count.
Yeah, but it was a long time coming. I don’t think it was particularly hidden by the time she turned all veiny.
Giles, on the other hand… that vicious ass-beating he gave to Ethan Rayne in Halloween came out of nowhere. Prior to that, we hadn’t seen him hurt a flea.