To have gained a rapport with a person of the desired sex only to have it quashed by saying something that is ridiculous or overly 'nerdy' you kill the conversation.
Origins of this terminology date back to an occurrence on a New Zealand Contiki tourist bus in which a man was talking to a woman in a way some would call light flirting. All was going well until he started going on some tangent about how the Auckland bridge's original designs had etc etc. Hence killing the conversation. It is from here we take our term Bridging.
Person A: How's John going tonight?
Person B: He's been bridging all night.
Please Note: this term may be altered slightly to fit more grammatically into sentences.