Well, Willie was taken out of the house, which says clearly that he failed to meet his responsibility.

I looked at sort of like a bull fight. (Very rough analogy, not perfect.)

The matador taunts and provokes the bull into charging, then sidesteps. The matador is a participant and is an essential part of the fight. If the matador jumped over the rails and left the bull alone on the fields, there would be no fight.

I don't think Willy was unpredictable. They were all sitting around waiting for the volcano to blow. Willy had said he would get himself thrown out so they couldn't vote him out. Janelle was smiling/laughing when the explosion made them jump up.

Britney went and hid to avoid it.
Joe did not. If he felt threatened he could have gone to the diary room. He wanted to show that he wasn't intimidated, but he made a big deal of the exact contact Willy made because he knew BB would throw Willy out.

Willy deserved what he got, but Joe was not at all innocent looking to me, and I know that scene was heavily edited. But I guess you're right, he knew how to walk the line and avoid the consequences of crossing it. However, I don't have to like his behavior.

Bullying is finding the weak person. Willy went after arguably a well-matched foe. I would say that he picked a fight.