I freaked slightly, ran and grabbed my empty CD case and went to find my dad. I was like, "Dad! That tape you're playing, that's this **waves Achtung Baby case**, it's like my favourite U2 album!" Turns out, he had gotten a box of old cassettes from someone, and had been playing them randomly. When he put that one in, he didn't even realize it was U2. I went and looked through the box, and freaked even more hugely at what I found. Under A Blood Red Sky! I really freaked at that point, because I don't even have that one on CD yet, and thusly, have only heard a couple of the songs on it.
Those were the only U2 tapes in the whole box, and neither had cases, but I snagged them anyway (of course), and used the tape deck on my stereo for the first time in about five years (I'm not kidding).
YAY for randomly finding old U2 tapes!