In WW2 Bomber crews took flasks full of hot tea or coffee but were told by the older, more experienced crew to only drink it on the way back from a mission.

R.C. Rivaz DFC writes in his book, Tail Gunner, that he ignored this advice and drunk his tea on the way out. There was no plexi glass in the turret and it was -40C (-40F) outside.

On the return he was bursting for a pee so peed into his flask and tried to empty it out the window.

The slipstream blew it back onto him where it instantly froze.

He never did that again.