I always cringe when I see laymen discussing physics in comments sections of news websites. A typical situation: one commentator put together a sentence with all physics-sounding (kind of) terms he's ever heard of; the next commentator "agrees" with the previous one, adding something that sounds more reasonable (to folks who've never taken high school physics) but unfortunately violates the first law of thermodynamics; then yet another guy comes along and corrects both of the above in a pedagogic tone, with an argument that violates the second law of thermodymics...
I cringe even more when laymen discuss mathematics, but that's much rarer compared to physics.
Granted, mathematics (theoretical computer science included) and theoretical physics are probably the most abstract knowledge known to human beings, but I'm beginning to wonder if there are other professionals who would also cringe when I myself is discussing something outside my domain of expertise. Or when a better mathematician or physicist listens in on my baby talks with someone on the roughly same level.