The emo kid's mom went to jail because the kid was hung.
Emo Kid's Mom in Jail
Explanation
Explain Bear
Listen up, smart guy! This joke plays on the double meaning of "hung." It makes you think the emo kid offed himself, which is why the mom is in jail, but it could also mean the emo kid is packing heat downstairs. You probably don't understand any of this because you're probably shorter than Danny DeVito.