Its when you drink or eat something by accident that someone has previously spat sperm into after they've given someone a blowjob.
Eeooh Charlotte's just up jizzed herself again!! Lol
As I taught the students on how to pronounce 'foreskin' and as im female and due to some of them being foreign. We reached the point during the lesson where variations of the word needed to be shown. Among them was 'knob collar' as a slang variant.