Jelly or Jam? Peanuts, salted or roasted? What about salsa, mild, medium, smokin' hot gringo-killer? Well, whatever your taste, it really doesn't matter if you can't get the blasted jar open right? In fact, if you had a way to blast the jar open at least you could scrape your favorite jarred item off the fridge as it slowly slides into a puddle of glop on the kitchen floor. If only you had something like that. I don't recommend a power washer for this, it ruins the flavor of most things by obliteration.
In lieu of jar-blasting powder and because not everyone is married to a peanut-jar exorcist either, you get to play a fun game the next time you have a stubborn jar. Stop antagonizing the cat for a bit and go get a table knife, or a pair of scissors (even the horribly-inept-at-cutting ones work great for this). We're going to play a new game, called Whack-A-Jar. It is much like whack-a-mole, but slower, more fun, and you don't actually incur the wrath of PETA for suggesting animal violence is "entertainment." There is only one target, that dumb jar's lid.
This is a highly complex one-step process so you might want to grab a drink, and settle in for the long haul. Take you knife, scissors, or other heavy-ish blunt object (no your child's head does not count) and firmly whack the jar's edge with the blade at a 45-degree angle in about 3 places around the lid. Try opening that jar now, and you will make He-Man think he needs an engineering degree.
If we have any golfers here, you'll immediately realize that the idea is to actually make a divot in the jar lid. Not one that you have to replace, brilliant!
Why it works: The air-tight seal on jars is there to preserve freshness and keep products crispy. By whacking the edge you are breaking the seal, and removing its will to fight you when opening. This is also why they tell you not to buy jarred products with a dented or popped-up lid. Enjoy your new game!