A derogatory term similar in meaning to asshole, or stupid asshole. Jackass is a term that's almost never used by today's young people but somehow it sounds hilarious when an old person says it and really means it.
The jerk CEO at a nursing home was telling old man Smith that if he was going to stay at this nursing home he would have to sell his house and possessions or be kicked out.
Old man Smith: "Jackass!"
Nursing staff covers their mouths and tries desperately to stifle their laughter. Old Man Smith just said exactly how they felt about their CEO.
swooning teen chick 1: "omg, ryan is so fucken hot!"
swooning teen chick 2: "no! bam is!"
swooning teen chick 3: "uhh your both wrong; steve-o is!"
swooning teen chick 4: "johnny is the hottest of the jackass crew!"
*swooning teen chicks begin to argue about who's the hottest*
teen chick 5: *quietly* "hell, i'd do 'em all."