FYI - Personally I wouldn't put mayo on much of anything, but don't go to Dick's (in Seattle) and ask for a "special" burger. (minus mayo, catsup, etc). I did, and they looked at me like I was crazy. So I had to take it as it came.
I don't think that Dick's is even worth the experience. We have one here in Spokane, and I've never eaten there in the 10 years I've lived here.