Why do my old light switches feel loose and click weird?

The toggle itself probably has wear in the pivot point where it connects to the mechanism inside, which lets it move around more than it should. Over time that internal spring and contact get loose too, so you get that weird play and clicking sound instead of a solid click. Replacing the whole switch is cheap and takes two minutes - just kill the breaker first and swap out the old one. If it's an older house the wiring might be fine, but those switches don't last forever.

The click itself isn't always a sign of failure - sometimes it's just the contacts making noise as they wear. I had a switch in my old house that clicked like crazy for years before I finally replaced it, and when I opened it up, the actual mechanism was fine, but the metal contact points had developed a slight gap that made them clap together instead of sliding smoothly.