Bed Cred is the reputation you gain among your peers for sexual prowess (or not, as the case may be). Bed cred is not gained only from bedroom sex, it can be gained from sex in a swimming pool, tennis court, or for extra points, bondage on ITV primetime, or other live tv shows. Interesting positions and/or use of equipment can get you extra cred, but size is the main factor - a 1 foot wonder will always beat a 1 inch wonder. Just remember, word has to get round, or no Bed Cred can be gained.
Josh lost almost all his bed cred when he split up with Jane and she admitted he only had 3 inches