BSDD also known as 'Back Stabbing Designated Driver' is referred to person who is set out to be the designated driver in a situation where his/her friend are already planned to get wasted that night. The 'BSDD' is known to get drunk first on purpose leaving him/her incapable to drive having him/her's friend out to be the new 'unplanned' designated driver leaving that person to stay sober for the rest of the night and missing out on loads of drunken fun him/her had planned for the weekend.
Brad: Sup, man. How was your birthday weekend? I know you've been waiting to get wasted allllllllll week!
Todd: I was sober all night. God damn Tommy ended up pulling a BSDD.