In the scene in The Full Monty where Gaz and Dave find Lomper (the ginger guy) trying to commit suicide in his car, his skin is bright pink. That's a telltale sign of carbon monoxide poisoning, although it's not clear whether that's what his rescuer (Dave) noticed, or if it was the rather more obvious fact that he was sitting alone in a parked car full of smoke with the windows up...
Probably the latter, as Dave lights a cigarette as he walks away from the car. As soon as he does this, he stops and rushes towards the car to pull him out.
