1. An exclamation point (!). Bangs have various significance in computer languages. In boolean logic, a bang can be shorthand for NOT (e.g. !x, !=). A bang in some languages can be used to denote the start of a comment line. In some cases, a bang is also used as a delimiter.
2. To fuck someone.
1. Bang-X is another way of saying not-x.
2. I should have never banged the chick with herpes.