There are plenty of allusions to sex in Macbeth and more times than not, they're about impotence and sterility. The weird sisters cast a spell to "drain" a sailor "dry as hay" so he won't be able to have children with his wife (1.3.4). Lady Macbeth insinuates that her husband is impotent in the bedroom when she goads him into killing King Duncan. In doing so, she also implies that "doing" the deed in the bedroom is like "doing" murder, which prompts Macbeth to declare "I dare do all that may become a man" (1.7.3). Macbeth says this, of course, right before he insists that his wife should give birth to male children only so, make of that what you will. (Or, check out "Quotes" for "Gender" if you want to know what we think.) Even the Porter's dirty jokes lead to a discussion of male performance (or lack thereof) when he laments that drinking a lot of alcohol puts men in the mood for a little fun but also makes it hard for them to function (2.3.3).