Thanks, L! I would guess that Lois would point out that, for all they knew, Superman was *not* a "mere mortal," and that, given his ability to levitate, he might well not even put his tights on one leg at a time. (And that's assuming that they even come off in the first place!) And, of course, just because most people can't handle having fans, that doesn't mean that *Superman* couldn't.
I'm sure she would attribute "C. Jerome Kent's" (whom she may or may not realize is Clark -- I don't think she knows his middle name at this point) attitude to sour grapes.
And I suspect that she would have a healthy (or, perhaps, unhealthy) dose of denial that her own mooning would fall into the category of "fawning."
In any event, I doubt that her behaviour toward Superman would change in any way as a result of the letter, despite what Clark might have hoped when he wrote it.
Joy,
Lynn
