A contact high? I'm sceptical about that term. According to most sources, it's psychological, not physical. Since it's second hand smoke, the air has been in people's lungs, the majority of the THC molecules would have been absorbed in other's people's blood already. So I don't see how it could be physical. I think we're more talking about subconscious psychological and sociological factors than actual effect of the **** here.
But anyway, when you feel messed up you shouldn't drive, that goes without saying. No matter if it's caused by alcohol, cannabis, coffee, contact highs, or just generally feeling bad.