Kooning means: You can flirt with, or hit on your friend’s serious girlfriend. This nickname is after the YouTube star “Koon”. Kooning can often be made when the boyfriend’s away. The girlfriend may show pity and affection for the kooning boy, but this is mistakenly misinterpreted by the despicable kooner. Kooning does not constitute cheating, as the girlfriend loves her boyfriend. This makes the act of kooning even more disgusting. (in Community Dictionary, added by Thingamajig)