Vanilluxe.
I loved Vanillite and Vanillish was even alright, but Vanilluxe made it one of those "boring just make it bigger or add a second head" evolutions, and being the third evolution, didn't do anything good with it unlike Deino whilst also taking away the chance for the two to get a third, actually decent evolution. It then proceeded to be bad in battle and wasted a slot on my team that I promptly replaced with Flygon. Now we can't get a cool chocolate banana split Pokemon, sundae, root beet float, or any other neat ice cream gimmick Pokemon, we just have two scoops of Vanillish except one is retarded and probably dropped on the floor who the fuck would eat this I can't even stick my dick into it, fuck.
Doesn't help that it frequently tarnishes the reputation of Gen 5. So now when people have nothing to fall back on, they can blurt out "HURR ICE CREAM POKEMON"