Sure he may pick on people weaker than him, but if he happens to realize his opponent can effectively kick his ass, either he will find a lame excuse to get out of it, or he’ll stubbornly refuse to back down and get his ass kicked just for the sake of form.
Don’t expect that to make him think twice the next time, though: the Boisterous Weakling shows an astounding inability to acknowledge his own impotence.
The thing about masking your weaknesses with false bravado is that it makes you look like MORE of a dunce to almost everyone else.
It’s so obvious and overdone that it’s actually got a full article on TV Tropes.
BOISTEROUS WEAKLING