Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic is titled "Funtime Activity: Pickup Lines That Only Sound Good" and shows a man at a bar saying to a woman: "Baby, if sexual satisfaction is a disease, I'm your cure tonight." The banner framing device sets up the premise that this is a pickup line that superficially sounds smooth but actually conveys the opposite of what's intended.

The humor lies in the logical implication of the line. The speaker means to say he will provide sexual satisfaction, but the metaphor he chose actually says the opposite. If sexual satisfaction is the "disease," then being the "cure" means he would eliminate sexual satisfaction -- essentially promising to be terrible in bed. It follows the classic structure of pickup lines that use "if X is a Y, I'm your Z" formulas, but here the speaker has bungled the metaphor so that it becomes self-deprecating rather than seductive. The comedy comes from the gap between the speaker's confident delivery and the inadvertent self-own embedded in his words.