I had a brief time when I thought suicide would be a good idea. It was when I was a kid with little personal autonomy, my life sucked, and I believed in an afterlife. But I wasn't depressed enough or determined enough to go through with it, and since then all three of those circumstances have improved. Now life is awesome.

Edit for clarity: There was very little chance I was going to do it. I don't have a biological tendency to depression, and I don't expect to ever be that depressed again.