Here are various "fixes" I've found:
Adding a bit of sugar or lemon juice (up to 2 tbl.)
Add 1/2 tsp. MSG
Make a dilution blend:
Make a simple gravy of a couple tablespoons of flour stirred into 3 or 4 tablespoons of melted butter, to which is added a 14 oz. can of beef broth over low heat until thickened to an appropriate consistency, then add 1/2 tsp of MSG powder during thickening. (Fat counteracts capsaicin - the irritant).
Throw in a chunk of chocolate (mexican chocolate such as Abuelita is great).
Blending in a little masa helps control the heat and serves to thicken a too-watery chili.
If you chili has beans, add an extra can of beans with their liquid (it has a bit of sugar in it, too).
Add a can of dark beer.
Serve with copious amounts of sour cream and cheese.