Found in hot peppers, chilis (sometimes spelt chiles) but not in wasabi.
Pure capsaicin is almost guaranteed to give you respiratory arrest if you inhale it (it's a white powder). Thankfully, pure capsaicin only exists in pharmaceutical labs awaiting incorporation into various creams and lotions. Perhaps paradoxically, capsaicin preparations are quite useful as analgesic agents - they numb the pain sensation. Even so, the concentrations used are lower than 1% - dangerous stuff.
A measure of how concentrated capsaicin is in nature, have a look at http://www.flyingchilepepper.com/facts.html