when one is hanging out with a female friend (girlfriend, random chick, hooker ect.ect.) and engages in sexual activities. (blowjob/handjob)
Then after ejaculation occurs, the person leaves without paying, or returning that favor.
"Yo man, i feel kinda bad"
"i was hanging out with my girlfriend today, and she gave me a bj, and then i left before she made me return the favor."
"ahh the good ol cum&run"