A short hand expression for stealthily stating that something excites you so much that you achieved an erection, or "Set my Dick on Hard". This is a thinly veiled reference to a Star Trek phaser where a person could set different power levels for that weapon, with kill being the highest setting. Settings one's dick on hard would be the highest level of excitement a person could generate via their phallus.

when you've done something so cringe you can't stop replaying it in your head and it stops you from getting on with your every day life