I've never had a fighter hesitate to answer, because they all know it's a relevant question. Just to cite a few recent examples, Duane Ludwig told me how much he weighs. Thiago Alves told me how much he weighs. Randy Couture told me how much he weighs. Frank Trigg told me how much he weighs. Miguel Torres told me how much he weighs. None of them hesitated or acted like it was a rude question.
The first fighter who ever refused to answer was Gina Carano, whom I asked last week. Here's the audio (via Steve Cofield) of me asking Carano how much she weighs, and of Carano refusing to answer:
Notice that Carano's opponent, Kelly Kobold, volunteered her weight (160 pounds) without me asking her. Kobold knows that it's a completely legitimate issue, as has every other fighter I've ever asked.
So why won't Carano answer? I don't know, but I sure hope she's telling the truth when she says she's going to make weight on Friday for her fight on Saturday. If she misses weight again this week, it will call into question whether she's ever going to take her sport seriously.