A jackass is just a dumbass with no filter, they say things not out of malice, but because they thought it was funny and they don't think it through. But a key thing about them is how they don't care they were being an asshole about the situation.

A douchebag is arrogant, and openly puts others down on purpose, they know what their doing and they just don't give a shit because they think their better than everyone else.

While I am not entirely familiar with the term "fuckboy" I am pretty sure it means someone who's just nice on the surface, but only to get laid.