I think next time you spot your friend doing this, immediately
approach him like giving him a tap on his shoulder and say "Hey,
how ya doing?"... then after that you immediately give him a
shocked face, like what the fuck are you doing? I cant believe you
actually got a fetish for this!!
Then your friend would probably feel embarassed and sorry for
his actions and know that it brought him shame and things like
this, hopefully he would wake up his ideas.
Maybe one day, after this "incident" you should also try to have
a talk with him on this and hopefully to guide him on the right
path.
