Which anti-fog spray did you end up using after that night? I've been skeptical too, but hearing about a real mess-up like that makes me reconsider. Foggy glasses can totally ruin moments you can't get back. Was it just the spray failing, or did you not have it with you? I'm curious if the brand matters or if any basic one does the trick. Also, how bad was the fogging? Like, could you see anything at all?
Honestly have you tried the shaving cream trick? Rub a tiny bit on the inside of your lenses then wipe it off with a microfiber cloth. Sounds weird but it saved a camping trip for me last fall when my glasses kept fogging up over the campfire. Way cheaper than the sprays and it actually works.