A thunder bomb is a poor man's drink that mimics the experience of a Jaeger Bomb, Vegas Bomb, or Irish Car Bomb without any of the costs or benefits associated with a real "bomb" drink.
A thunder bomb consists of a shot of Vladimir or similar cheap vodka dropped into a partially filled cup of Dr. Thunder which is subsequently chugged. This chugging is often concurrent with a heroic effort of withholding vomit.
A general rule of thumb is that if you are drunk enough to think that a Thunder Bomb is a good idea, you are far too drunk to have a Thunder Bomb.
"Dude, how drunk were you last night?"
"Drunk enough that I thought a Thunder Bomb was a good idea."