To continue building a joke up until it breaks down and leaves an awkward silence. So named because it is not unlike reaching the top of a flight of stairs, then putting your foot out for another step and stumbling because there isn't one.
"Dude, she's so easy a caveman could do her."
"She's the town bike!"
"So many people have fucked her, I got HIV!"
"... You just fucking top-stepped it, man..."
Bombshit is the marriage of the the terms "the bomb" and "the shit" only to emphasize the "bombness" and the "shitness" of oneself. This term should be used when the titles "the bomb" and "the shit" are not suffiecent because they do not capture the true quality of the person in the situation. It should be only used sparingly in order to preserve it's effect.