Put too much stress on the airframe and you'll explode. You'll get Over G warnings beforehand, so it's on you if you ignore it too long. LOL
Some planes like the F/A-18 have limiters that won't let you do that.
The SU-27 and SU-33 let you turn off limiter below a certain speed (180 knots?) so you can pull a Pugachev's Cobra.
(not my video, just one from youtube)