I work for the USPS, and I occasionally see some pretty funny stuff written on envelopes. One time I saw a letter being sent from someone in jail to his girlfriend. I assume he intended to use the word "sweet", but what he wrote on the envelope was "To my sweat tasting cookie that I love"
Lots of interesting misspellings of the word "deceased" as well when people are returning mail to the sender. I've seen people described as being "diseased", "desist", "decreased", and in one instance- I kid you not, "degreased". Also, I saw a letter last week marked "Return to Sander" so I asked my boss if we had a carpentry department I wasn't aware of.