So I just loaded my PayPal with $20 that I wanted to use to buy some BTC because the price dropped and I wanted to buy in because I know it's going to shoot back up.
I sent my regular exchange guy the $20 and gave him a Bitcoin address. I hadn't received a payment, but he said he sent it.
SO WHAT HAPPENED?
When I opened MultiBit I was on the 'Send' tab. I didn't check that. I had a Bitcoin address already in the Send input box from when I sent BTC to someone like a week ago. I ended up copying and pasting that address and sending it to my buddy for $18 worth in Bitcoin.
Should of payed attention and clicked the 'Request' tab so I could get MY Bitcoin address.
MORAL OF THE STORY
Don't send your exchange guy the wrong address on accident. </3