For a serious answer, here you go: First of all, yes, it's all in your head. (the big one) BUT, what others have said here, thinking of something else, servicing yourself a few hours before, they all work.
Here's a quick fix that I found by accident: They make condoms with something inside that desensitizes you. And they fvcking work. My wife recently had a baby, and she isn't on birth control again, yet. So we have to use protection. I felt like a kid, going into the story to get rubbers. Hadn't used them in god-knows-how-long. So I pick up some lubed ones, not noticing that they're also "male desensitizers", at least until I got home. No biggie, I'd been cut off for months anyway, I figured that couldn't hurt until I got back in "shape" again.
Let me tell you, my wife has to run me away now. You put one of those on, and you're ready to drill for oil. Your back will give out before you're done.
You want a quick fix, try that.