relative to facebook, a "tag bomb" occurs when a person is tagged
in an ugly/awkward/compromising photo they obviously do not want other people seeing. Bombers should write "tag bomb" in the comment box, or gloat in some way, so that the picture comes up in newsfeeds everywhere.
For maximum effect, "tag bombs" should occur so that many people see the photo before the victim finds out. This means tag bomb when friends are at work, on vacation, or otherwise preoccupied.
Tag bombs should be in good fun. Tagging a naked photo of you friend might not go over too well. Unless you hate your friends and want them to hate you. Then do what you will.
Rambo and Cole take a picture together--the photographer zooms in to get a good head shot. Cole looks fine, but Rambo has a giant thing of lettuce in his teeth, clearly visible.
The photographer uploads the picture onto facebook and tags both people. Rambo immediately untags himself, for obvious reasons. Cole realizes he's the only one still tagged and asks Rambo what's up. Rambo explains he looks stupid and doesn't want people seeing it, and even though he asked photographer to take the picture down or crop him out, photographer wouldn't do it.
Cole waits for when he knows Rambo will be at work. When the time comes, he tags Rambo who won't find out for 6-8 hours, then writes "Tag Bombed Baby!" in the comments section, for good measure.