West Adams, South Central, Watts, Boyle Heights, Crenshaw, Leimert Park, Pacoima, Sun Valley, and parts of damn near everywhere else. North Hollywood is not dangerous, Compton isn't a neighborhood, it's its own city, and most of the shitty parts of Pico and Olympic are in West Adams (i.e., Pico-Union). While Mid-City and Echo Park aren't exactly the best place to find yourself alone and drunk, they don't deserve to be considered "most dangerous," because there's a lot of decent folks mixed amongst the assholes. Hollywood doesn't even make the top twenty most dangerous neighborhoods. There's crime, sure, but to compare it to Compton? Dude, where are you from?
These places aren't uniformly horrible, either. Except, maybe, Watts. I've never seen a damn bit of good from that place.