Performing "The Unthinkable," then you put your dirty wang in her mouth.
See above for "The Unmentionable."
A man takes a shit, then freezes it for a week or so to get it good and hard, and another man uses it like a dildo on the other guy.
Gay guy 1: I want to do something freaky.
Gay guy 2: How about THE unmentionable?
Gay guy 1: I said freaky not fucking disgusting.