I think Jayne sees rejection at every turn. He ran from Serenity before he could be rejected there, he drank too much trying to fit in with the slaver crew and ended up in fix they obviously just left him in, now Mann is rejecting him. This all fits in well with what you're telling us about his past. Jayne tries so hard but it never seems to be enough. I'm looking forward to him finding out his family on Serenity haven't abandoned him.