Most inhalants, but the whole balloon method isn't going to deprive you of oxygen if you also breathe real air, and if you get so out of it you pass out and release the balloon, it safely escapes. It's the idiots diving headfirst into garbage bags inflated with it that are in real danger, and people who have so much they do it until it sucks all the B12 out of their systems, and THAT causes potentially permanent serious brain damage. I'd imagine vegans are at even more risk of that than hamburger eating hippies.
The Galaxy Gas shit seems to be specifically marketed for recreational use and packaged in such a way it can't be done safely without risk of freezing your lungs or actually causing anoxia (and thus possible brain damage directly rather than indirectly). Apparently it's usually used by just directly sucking it out of a pressurized canister? Even the Deadheads (and I assume Phish fans) who were and are huge fans of the stuff would always do it from balloons, not straight from the canister.