I'm very large-built guy (big rib chest and about 6'4") but skinny, and I never really have problems with people
The only time was when a Nazi called me a 'gothic asshole' (In English which was weird), or the time I hung out in a fascist bar and someone through a screwdriver at me, but I suppose I should have expected it. Spain has a pretty strong underground radical political streak.
From the mainstream mundanes in Spain, I usually get "It's Marilyn Manson." I look nothing like the guy, his music's pretty good, but I most definitely find it more of an annoyance than a compliment to be likened to him, in compliment or in jest (and I've gotten it in both).
One of my friend's parents said to me one time, "You know, when you came to the party we thought you would be the one with the bad attitude. But now you have been so polite and charming, that we realized we misjudged you." When the combination of my garb and my demeanor has adults apologizing to me, I know I must be doing something right. It's like spreading enlightenment one person at a time.