I've used the spoon trick for the longest time, until I was found faced with the challenge in complete lack of spoon or similar instrument. Then I looked at th

I've used the spoon trick for the longest time, until I was found faced with the challenge in complete lack of spoon or similar instrument. Then I looked at the cap and realised it has this wedgy shape slightly protruding. Well, hold the jar strongly in one hand and hit that part hard with the ball of the hand near the base of the thumb. This deforms the cap just enough that air gets in. Might take a couple of tries to get the hang of it but has worked for me ever since: I've never used the spoon trick again since at least a decade.