Is it normal to want to have sex with my wife's best friend?

So what's the problem? Go ahead and do it.

The running joke I've always heard is, "When I ask if I can have a threesome with your best friend, I'm only joking.

Unless you say yes.

In which case, can I video it?"

Since she already jokes about it, you can try to gently approach the subject, and who knows, she might go for it (of course, her friend still has to go for it!). But like randomjelly noted, this can sometimes cause irreparable harm to a relationship, so proceed with caution and a lot of conversation, and be prepared to drop it quick if she suddenly turns squeamish.

A synonym for threesome is divorce.

Certain death; is screaming from the sky.

I agree with YBNormal. Go for it!