First, I never try to hide my girly purchases stuff under other stuff I'm buying. That may be a sign to any other shoppers who see you doing it that the pretties are actually for you.
Second, at a clothing 'rack', and more often in the check out line, I will hold the garment up a bit as if inspecting it for defects, letting all see me do it. I figger they will think that my purchase is actually for a female and not for me. If a female is behind me in line, I may turn to her and ask something like " do you think it's pretty or do you think she'll like it?" I believe doing these things disarms those who would wonder.