Stupidest thing you've done on Steam?

Just did mine today.

Bought the Rockstar Bundle on Green Man Gaming this morning, already owning some of the titles. I then proceeded to activate the keys for the games I didn't own and was left with some spares. Rather than copy/pasting my newly spare keys straight into into the file I keep them in, I decided to check them first.

I often try keys for stuff I already own, looking for the "Product already owned message" just so I can see that the keys sent were for the correct games. Well, I'll not be doing that any more! Already owned Max Payne 3 and you can imagine my surprise when my Max Payne 3 key actually activated.

Turns out I had a Max Payne 3 (ROW) on my account and this new key was for Max Payne 3 (WW). Whilst I knew there were different regions, I didn't know you could actually activate 2 keys of the same game from different regions on the same account. Total waste of a key. Lol, what an idiot.

So what's the dumbest thing everyone else has done? Anyone else been as stupid as me?