All the better ones had that button, usually named "degauss". My 22" flat CRT (it was flat on the front, like LCDs today, which was a great feature at the time, but made the thing extremely expensive and extremely heavy) had a degauss function that was apparently so powerful it visibly distorted the image on other monitors right next to it when I degaussed mine. I made a joke of doing that in the middle of games on LAN parties ;-) didn't work repeatedly though, after degaussing once I had to wait for some time until degaussing again would actually do something.

I made the mistake of pressing Degauss on a monitor while holding a magnet next to it.

This basically calibrated the thing to look normal... with the magnet there. It took quite a while to restore to normal.

I finally replaced my aging CRT at work (3rd screen for unimportant stuff) after it finally died after 20 years of service. I still miss pressing the degauss button, which (perhaps relatedly) needed to be pressed after powering on and sometimes multiple times during the day.

Numerous monitors had degaussing features, Sony's among them.

And if they didn't, and somehow you managed to magnetize it, you needed to use a degaussing coil, moving it away from the screen in a spiralling motion... ah, the memories.

https://www.youtube.com/watch?v=3pVLizAHby4

I assume that by "somehow managed to magnetize it" you mean "had crappy detachable boom box speakers sitting on top of it in college, causing the TV to eventually display distorted blobs at the top edge of the image".

No? Huh, guess it was just me ;)

I honestly don't know. I picked up a Compaq monitor with a magnetized grille from the trash in 2002 or so, and used for my secondary pc (a venerable P200 MMX that took a LONG time to recompile the 2.4 kernel on a then-unstable Debian Sarge).

No idea how the previous owner managed to magnetize it, it never happened to me.

I did that, and figured out if you flipped the speaker around, you could "paint" the distortion away.