lame: laughter, followed by: "dude, that bumper sticker is hilarious."
as for good ones, whenever we'd take a long drive somewhere, my intensely catholic 90 year old italian grandmother would (at least once per trip) look out the window and utter: "this must be where god left his pants." i still have no idea what that means, but i do try and crowbar it into my everyday life as much as possible. i should also note that a "long drive," to her, was 20 minutes or more (sometimes less.)