i have a 5 month puppy and he keeps sniffing peoples private parts and bottoms any ideas what i can do

Take him to one side and have a little *chat* with him. Explain that it really isn't on and would he kindly desist immediately or you will be required to take preventive action :D that should do it. Failing that try giving a firm No and check him. If that fails try a lump of 2 x 4 ;-)