I had that same problem, only it was some young adult sitting in the same aisle as me. He seemed mentally retarded or something. He would scream out things, repeat the dialogue, laugh obnoxiously loud at serious scenes, and wore the popcorn bucket on his head. I always get the morons in the same theater as me.
Besides that, I liked Heath way better. He played the perfect crazy guy, and had you totally wrapped up in the movie. Sometimes I forgot he was acting. I dunno what you guys were watching, but I thought the joker was crazy in the cartoons as well. Just because he's named "The Joker" doesn't mean has to be funny and goofy.