Verb - The action of catching a man off-guard by squeezing their balls to inflict sharp pain. Often as a prank or means of revenge.
"Kevin was about to confess to his crush when I ran up and totally grabmoed him! Funniest shit I've ever seen."
Grabmo is a the act of hit an run squeezing a mans balls as you pass by them in public or elsewhere. Usually women use it to inflict pain and are gone before they are caught or do it in situations where the man should not react to pain such as funerals.
"I was trying to introduce myself to my professor when that dumb bitch grabmoed me and I made the dumbest face in front of him. FUCK THAT BITCH" - Spicy Gazebo