Ghostin' is when you leave the bar, party, barbecue, etc. WITHOUT telling anyone.
The 'ghoster' usually says he/she is 'going to the bathroom' or 'going to buy a round'...but then they leave.
Hey where's Jon? I thought he was going to the pisser...is he ghostin' again?
Hey did you hear that Dwight ghosted us at Billy's the other night?