Some people like chili, others don't. Capsaicin makes chili peppers spicy and even burning. The strength of chili peppers is measured in scovilles. Pure Capsaicin is measured at around 16 million scoville units.

Chili on wikipedia

The hottest chili right now is a hybrid chili pepper called Naga Viper. It is measured at around 1,3 million scoville units

Okay, time for some chili eating videos:

Naga Viper tested:

Naga Morich (around 1 million scoville units) eaten by a bad ass: