To leave a party or other social gathering without being detected. Usually the other participants do not realize the departure until some time later. black-fogs, black-fogging, black-fogged
Origin: "black fog", something never seen
-"Hey, where's Bill?"
-"I dunno... what, did he leave?"
-"Looks like he black-fogged!"
"Brian got caught last night trying to black-fog. He's usually really good at it, but Carrie saw him walking to his car."