Check out this hilarious pie-chart from MadAtoms.com, about what men think about menstruation. It's pretty on point, especially the 12% of men that think periods are dangerous- because they attract bears. I once asked one of my buddies why women aren't allowed to be Navy Seals, and he replied, "Ya know how many missions would be compromised by sharks that were attracted by periods??" This boy was DEAD serious. For shame!
These bizarre ideas about periods are examined in Emily Martin's essay, The Egg and The Sperm: How Science has Constructed a Romance Based on Stereotypical Male-Female Roles. In this essay Martin discusses the language that our society uses to discuss menstruation and how it perpetuates gender biases and inequalities. This essay was eye opening for me, and definitely something you have to read.