A shambam is the product of dating ambiguity. When a man believes he's in a relationship with a woman, but has not yet consummated said relationship by rounding second base, then a shambam may occur. Typically, a shambam will involve a club night, where the man will accompany the woman to a venue believing they will leave together. But the woman, believing herself to be unattached, hooks up with another guy and spends the night with him. For our unlucky bachelor, a shambam has occurred.
Mark hooked up with Iris? But I thought she was with Jordan? I guess it was just a shambam.
You mean she slept with Dan? But she went out with Adam last night. I guess she really shambammed him.
When you win an argument, Or get one over on someone.
Eg. "Dude, she just totally shambammed you!"