Kerst is also a term expressed once you have reached a climax of heterosexual intercourse in the mouth (blowjob)
"Hey, Ho! How much for a kerst?"
"Um... Excuse me Officer, that man over there kerst me last night"
"So your saying he screamed out kerst?"
"No nigga, he wrote his name all over my back...therefore he kerst me"
"Bitch please, I've kerst you before, see...right there!"