After reading the thread about the pram I was inspired to ask for other stories where someone has been really brazen.
We're lucky/unlucky enough to live in a University town which is also very tourist-y. This means everyone wants to come and "visit" us every time it's holiday time. Worst one has to be someone we met 10 years ago on holiday (and I should point out this was a Club 18-30 holiday) who we promised we'd keep in touch with and never did. Last year we came home to them standing outside the door saying "Oh I bet you don't remember us, we thought we'd finally visit!"
They also brought their two kids and dog with them. They stayed for A WEEK because both me and DP were too polite to kick them out. To this day, we've still no idea how they found us.