i fucking hate that bastard; when he leaves to go to the toilet, i'm helmet rimming his fucking glass
when one, driven by resentment/hate/anger etc takes the decision to rub their penis head round the rim of target-person's drinking glass as act of revenge
"i fucking hate that bastard; when he leaves to go to the toilet, i'm helmet rimming his fucking glass" What is the definition of "helmet rimming"?