For a while a few years ago, kids around here wore Rosaries as jewelry. I would comment very perkily, ask if they were Catholic, if they prayed the Rosary, offer to get them a copy of the prayers.
Oddly enough, the kids stopped wearing the Rosary as jewelry…
Anyway, you might be able to use his idea that he is religious to help him. When he uses some bad language, ask him if he thinks that the Blessed Virgin would like to hear one of her children speak like that? See if he has a Rosary, invite him along with you to Mass and/or Confession if you are in a position to do that.
But make it very light! be more inviting than admonishing–who knows what his religious training has been, what his situation is.
And of course, pray for him, esp when he’s particularly annoying.