Dedalus
Mercurial and fleeting
I thought it was pretty cold to leave the hitchhiker behind like that but I do understand it. I couldn't do it myself; I am a big softie and probably would not survive in a zombie apocalypse.
I wondered why they didn't at least slow down and tell the guy to turn around and start walking the other direction - towards the prison (since they definitely wouldn't pick him up on the way out to pick up more guns - too risky). But they could have picked him up on the way back. Giving him that information may have inspired him with some hope which in turn may have helped him stay alive - the guy was obviously really desperate.
That being said - this is the group that just tossed out some really sane, good people who could have really helped them out. So it wouldn't have made any sense to have them show compassion towards another stranger just a week later.