To pull another persons shorts or pants down. It works effectively if their is a gathering of people to see it and thus causes higher embaressment for the victim. An added bonus is if you are able to get a hold of both the pants or shorts and the underwear, causing their lower body clothes to be round their ankles. Does not work if their shorts or pants are tied so that ability to deebag a person is dismissed.
"Oh my god. You'll never guess what happened to Paul just then"
"Harry just deebagged him. LOL"