Normally I keep a roll of duct tape in my car because the stuff is pretty darn useful for a lot of things. While visiting Old Man Cactus Nursery*, I managed to rub against a cactus, and the lady helping my husband and me told me about this trick.
*The nursery is generally not open to the public, but we were allowed to visit after setting up an appointment. I think we bought a lot more than if we'd ordered online because we were there in person, and everything looks a lot more tempting when you can see it right there and be able to own it right away... DANGEROUS!
Step 2: Apply and Rip
Rip it off!
Re-apply as necessary.