A very difficult maneuver requiring the participant to go through the motions of eating a girl out but with your chin. This term is most commonly referred to as chinning or chin. The crimson chin is when one chins a girl who is on her period causing the blood to be stained on the chin, leaving a crimson hue on the chin, dubbing the crimson chin.
Yo dude you can still see my crimson chin from last night
1. v. to eat a girl out while she is on her period.
alternatively,
2. v. to throat-fuck an individual to the point that your balls slap against their face with such voracity that their chin becomes chapped and red, thus giving them a "crimson chin".
Daringly, these two actions can be performed at the same time to result in what can only be described as potentially one of the leakiest sex acts.
"I agreed to let Susiecrimsonchin me, only if she let me do the same to her."