Skullclamp
A skullclamp is a fiercely painful erotic act in which one partner inserts his head into the urethra of the second parter (obviously male) and then has the second partner attempt to squeeze the first partner's temples with his penis while fingering the anus of the said first partner.
Dude, me and Zack tried the Skullclamp last night." "yeah, how'd it go?" "well, he'll be out of the hospital by noon tomorrow......