One word that strikes fear into my heart... Humbler.

I had one Domme who just loved to put me in a humbler and then taunt and tease me with body worship. Her favorite was sitting on the bondage table with me on my knees on the ground below her with both my cock and balls trapped in a humbler. She would bring her legs close to my lips and then make me strain to kiss wherever she wanted. Sometimes she would even allow me to get to her panties IF I could stand the intense and sickening pain from basically being straight up (usually this was just a kiss or two before being smacked in the face and being called a naughty boy).

Simple yet very effective predicament situation.