Make organic chemicals. See ‘C1 chemistry’. CO is one of my favorite substances to get in designing chemical factories in space.
Toxic to who or to what?
Huff it to get high
Assume you were thinking of nitrous oxide N2 O.
C O is deadly when inhaled
And not even fun before that. People suffering from CO poisoning don't realize anything is wrong, they just die. Which is why we all have CO monitors now.