At some unknown point this unnamed man was possessed by the demon Marco. While possessed by Marco, he was shot in the heart and mortally wounded though Marco's presence in his body kept the man alive.
After the Winchesters captured Marco while he was trying to kill Goldie Schmidtlapp, Sam suggested exorcising Marco from his vessel in order to save the man with Marco promising not to tell Crowley what happened if they exorcised him. However, Sam spotted the bullet wound and realized Marco's vessel was beyond saving. Dean then proceeded to kill Marco with the demon-killing knife, killing Marco's mortally wounded vessel as well in the process.
After killing Marco, Dean drops the man's body off in a hospital parking lot, though he jokes to Sam that it was a school playground.