I can think of one kind of offensive reply “because I’ve been fucking your wife and sister from morning”
“I’m just super constipated.”
I like this one best, really.
“I wouldn’t be work’n if I wasn’t sweat’n.”
“Exertion. You should try it sometime.”
“I’m not sweating.” (Who you gonna believe - me, or your lying eyes?)
“I was watching COPS”
Profuse sweating when there is no apparent stimuli causing it can be a sign of serious cardiac issues. Perhaps he was just concerned.
If I didn’t particularly like the person, and they had no power over me, I might say “That’s kind of a personal question, don’t you think?” 
“I’m allergic to assholes” is probably too aggressive.
“Working hard. How about you?”
or “I have a high operating temperature.”
“Why does your face do that?”
In the words of Major Charles Emerson Winchester III: “In the first place, I do not sweat; I perspire. In the second place, I never perspire.”
Go with this one. Pretty much guarantee he won’t ever mention that again. He’ll probably stay away from you for good. Does your boss have a good sense of humor?
“Ebola. Would you drive me to the hospital?”
Horses sweat. Humans perspire. I glow.
Okay, I’ll ask: dope1, why were you sweating on that occasion?
I can’t help it. I have leaky skin.
Oh, that’s urine.
But don’t worry, it isn’t mine.
Nope not only she doesn’t has a good sense of humor but the guy who asked me the question is kinda her favorite.