When you're getting a blowjob but are too drunk to finish so you pee a little in her mouth. This is of course an attempt to fool her into thinking the fellatio was successfully completed so as not to hurt any feelings.
A: "Dude, I was getting a hummer last night but was super drunk and just wanted to pass out so I led her down the Yukon Trail.
B: "Did she strike it rich?"
A: "She thought so but it was just fools gold."