Ugh, my "thank you"s tend to be so quiet that I get the glare too. Siiiigh. It's usually because I don't speak a lot, except at home or when teaching, so when someone opens a door for me, me trying to thank them could be the first words I'd said for hours--so my voice is rough from mild disuse.

(The red pen doesn't know how to spell "sarcastically" or "sardonically"? Silly!)