Theoretically, someone could get the bends but even that isn't instantaneous. They'd fall over in pain and might possibly redden a little after about twenty seconds or so, but otherwise it would be slow suffocation.
Unless they try to hold their breath, of course. Then they risk a lot of internal damage, but again it wouldn't be all that spectacular to look at.
He was pretty much the punching bag of the whole show, wasn't he? Like, I remember an episode where he turned orange from eating too many carrots (magical Ms. Frizzle carrots, of course).