Question about revoking a father's rights?

Okay, So before anyone gets the wrong idea..this is not some angry woman or man hater. My sister's ex husband has just completely gone crazy or something. He has lost his job quit paying child support, is never home on his weekend with their child. The grand parents have him a lot. These things wouldn't bother her, but he recently joined a band at the age of 30 I might add and starting going out drinking. He tried to take their son with him to a bar and the bouncer turned them away, My nephew told his mom. He curses horribly around their son and plays loud horrible screaming music. He has the worst temper ever and their son is afraid of him. He even took him on his weekend to stay with some friends for a party and their son told my sis(his mom) that he hid under the bed a lot from the strangers and all. We are sooo worried. He recently tried to take him to a gig where he was playing and was just going to let his son wonder around unsupervised. He is only just turned 10. We are sooo worried about him. My sister doesn't know what to do. If she can get his visitation taken or have him with only supervised visitation. Please help! Today was a soccor game and he cussed a childs parent out in front of their son. He also told my nephew that atleast you didn't make that last shot then it would be your fault your team lost. He's just a horrible person and bad role model, but we are also worried about where he takes him and who he takes him around. Please help. If you can give any advice on legal action. Thanx.