One who is of bitch nature as they attempt to invade another's buffer seat. This person is usually of jackassnature as well or known to be full of shit.
Guy 1: Hey did you see that jackass who sat next to me in seminar? Who the fuck does that?
Guy 2: Yeah that guy was a complete buffer seat bitch.
The person in a group who isn't a leader, on the contrary, because this person is a bitch, all this person does is take orders and defer responsibility to the actual leader. For this reason, this person never has to deal with anything that resembles a "high pressure" situation which- at least in their minds- is good because a high pressure situation would cause this person to crack and undoubtedly fail.
"'Did you guy's hear about LeBron James goin' to Miami to play with Dwayne Wade?'
'Yeah I saw that SI cover where LeBron is standing behind Wade. LeBron is such a back seat bitch.'"