shortened version of "Banter-Vortex" this occurs when something is said in conversation that stops the conservation dead. This is often due to "bad chat" that does not merit any responce from anyone else in said conversation. Bantexes are often noted for an extended period of silence after the bantex moment, which may feel like all the atmosphere is being sucked out of the room.
"did you see Peter Crouch's goal celebration Roger?"
- "yes I did William! did you see it Martin?"
- - "no, but i ate a prawn wonton"
(extended period of awkward silence - the BANTEX)