Is a muscular woman more threatening than I thought...
Yes.
are people just insecure...
Yes, that and close-minded to art (to anything, really) that doesn't fit the prescribed parameters of what they like to look at...
or is a big bicep perverted...
Sometimes it can be...
...and a big breast ok?
Yes, more often than not.
A person drawing a man in tights and wearing a cape is not asked "What are you, gay?"
That would depend where you display said "man tights", and how the figure is drawn. Maybe you haven't experienced it yet, but there are people who believe "superheroes for adults" has homoerotic undertones.
...but a drawing of a muscular woman gets "Whats with you and muscles? Are you a perv?" I am simply amazed. My question is have any of you encountered this kind of muscle-phobic (new word I just created) uglyness and is this a common response.
Clearly, from the lack of responses, you are the only one.
It's happened to me on the street!At some point, artists and photographers who deal in images of hyper-muscular women are going to have to accept that the image (or the presence) of a woman with muscles is provocative (clearly many of the respondents have). Exactly what is provoked in people
cannot be controlled. It shouldn't be worried over too much, but it should be anticipated. We can't afford to be naïve.
SinD, if you become serious with art beyond doodling

, you will be forced to develop a tough skin--a layer of armor (hmm, muscles...body armor?) that should remain in place even after you become "good."
Not having seen the doodles in question (that's not a request for a link, just a statement), the query are "You are perv?" (while admittedly not politely phrased) may not be an invalid one, as there
is a difference between drawing women bodybuilders as they appear in reality and drawing them as sexualized inhuman giants with the fantasy watermelon-shaped breasts out to---------------------->here (I know, because I've done both). There is a difference between drawings intended to titillate (no pun intended), and drawings where arousal is not the primary intention of the artist (I can't stress this enough because I think all of us who draw have done one or the other at some time or another). To claim that every drawing in the "genre" has the same intention toward the viewer would be disingenuous.
One can draw women with muscle as fetishistic material or with any number of other less controversial subtexts. But how many of us do the latter as opposed to the former?