If you like it hot (as in hot peppers) but exceed your tolerance, taking a swig of milk can counter the “mouth on fire” sensation. The spiciness of chili peppers comes from capsaicin, a chemical that binds to receptor cells on the tongue, called TRPV1, which send a “hot” signal to the brain.
As explained by a researcher from the Chile Pepper Institute at New Mexico State University, a protein in milk, casein, disrupts the capsaicin-TRPV1 bonds, thereby extinguishing the fire. Ice cream, cheese, and yogurt are effective, too. Other remedies that help, but less so, include carbohydrates like bread and sugar.
But don’t count on alcohol or water: They just spread the capsaicin through the mouth.
Also see How to Handle Chili Peppers.