Aaron Marino of alpha m. presents exercises to avoid for those men who have big legs and butt. Alpha recommends to completely stop lifting weights with the legs.
If you really want to workout the legs, you can do some squats, lunges, light weight leg extensions, and light hamstring curls. However, the goal is to not get any more mass on those legs and butt. Increase cardio by walking on incline, pedaling bike, and elliptical to reduce body fat as well as tone & shrink legs and butt.