Their responses are due to low self-esteem.
I doubt thaty seriously. I red what Nessa said, and I agree 100%. I never knew how to take a compliment in the past because at a younger age I struggled with low self esteem. I was always the biggest, tallest, and -est of anything else you name. Kids are cruel, so what was fat to them in High school, is a thick brick house in my adult life. Having short hair was always talked about in high school, but now, people be on my hair like crazy...
So when I became of age, and fellas would compliment me, I didnt know how to take it... "Girl you have beautiful legs mmm mmm mmmmmm" but in high school "You got big ole manly muscly legs... ugh" I can leg press 500 pounds easily. I took kick boxing, and modern dance, so I have VERY athletic legs, and I always thought they were ugly... Now I am a bit older, and I love my legs, so I now Know how to take that compliment...
My best friend and I were at Old Navy a couple weekends ago, and she and I were talking about how when your hair needs to be done, thats usually when people compliment it the most... and about ten minutes later we went to the Foor Locker and this dude complimented her hair, and she chuckled... He said, "Did I say something funny?" and she said "No, my friend and I were just talking about my hair, and its funny you mention that it looks nice, cause I think it needs to be done..." She told him out whole convo.
She does NOT have low self esteem. I mean, men here at work tell me that they like my toe polish, and I have said "Aw, and I just chipped the paint..." or something to that effect, without realizing that its a compliment, and not say thank you. I dont have an issue with my self esteem (as an adult), more so, I definitely dont have an issue with my appearance.