This is a sexual term referring to a particular sex act where a man receives a blow job from a woman, cums in her mouth, and then the woman (or could be a man) pretends to swallow, then turns to embrace her partner in a passionate kiss, thereby open-mouth kissing him with his own cum in her mouth. Hence, San Francisco Switcheroo (almost gay, not quite)
Man: You gonna swallow right?
Woman: Of course
Man: You better not pull a San Francisco Switcheroo on me cause I'm not okay with swallowing my own cum.