Not just fast food, but most restaurants in general. For someone who prefers a little kick, it's like the majority of bars serving only virgin cocktails. I made the mistake of asking for my meal to made a little on the spicier side(1) at one of these americanized mexican comfort food places. The waitress looked at me like I was asking her to calculate a double integral.

(1) This is common at Thai restaurants, so I figured I'd give it a shot.