It comes from the word mathematics (notice the plural), and because it talks about a whole range of processes, math is wrong.
As an American, I would argue that the word "mathematics" is wrong and annoying. Math refers to the concept and is all-encompassing and universally disliked. But "mathematics" seems to refer to a collection of individual mathematical processes, of which there are many. Which ones is he talking about? Don't know because he didn't specify. But if you say "math" then you know he's not referring to any process in particular and simply generalizing the entire field.
Examples:
Math sucks. (The entire field and everything in it is disliked, which of course is always the case)
Mathematics suck. (Which ones? Which problems is he referring to? What concept is he talking about?)
Therefore, Math should be the proper term to describe the discipline as a whole. Mathematics should be used to describe given processes, theorems, equations, etc.
Britishisms:
Trousers (Pants)
Biscuits (Cookies)
Pavement (Sidewalk)
Lift (Elevator)
The word trousers doesn't bother me. Often the various words for "pants" refer to a specific type or style of pants.
The more annoying thing is why
all these words end with an "s" despite being singular. It's not like you can walk around with one leg covered. Both legs are included by default, so the "s" doesn't make sense.
Biscuits are biscuits, cookies are cookies. British fail.
Pavement is a very general term that describes any surface paved smooth with any type of hard, rock-based mixture. But a sidewalk is a very specific type of paved surface, usually placed next to a road (side) and intended to be walked upon by pedestrians (walk). British fail.
Calling an elevator a lift makes sense, because it lifts, except for the fact that
it is literally called an elevator. That's the name for it. British fail.