He basically threw a piece of himself at Vegeta, once Vegeta got hit it wrapped around him so he couldnt move.
I dont know if this has been discussed or what not since I hardly visit forums anymore but heres what I think oh how Buu's body part attack should look like.
Basically, he takes a piece of himself and throw it like a ball, doesnt have to be like Buu throwing his right arm at you. Maybe have a speed of Krillin's Distructo Disk, not too fast and not too slow.
Then the following can happen once your hit.
a) You enter power struggle, while in power struggle, you cant move and you drain 5 points of health per second until you break free(winning power struggle) or you get hit by melee or beam.
b) Once hit by body part, you get blinded/frozen/stunned/or what have you, just to make it so that you cant move for a duration, depending on how much you charged the attack(maybe at full charge, the body part will be stuck on you for like 5 sec max, enough time to get bashed in). You are immobile(cant atk or shoot beams) just run and jump and teleport.
c) Make it like an effect like Trunk's beam(the 1 that blinds u). But instead of being blinded by a white light, your just immobile for a split sec or a sec, enough time for you to be hit with melee or a quick ki bolt or gen.beam.