Not as bad as some of these, but...
When I was a student a friend from home came to stay for the weekend. I had a two bed flat and was letting out the second bedroom to another student, so I said this was fine, but she'd either need sleeping bag in the living room or to share my double bed. Fine, we're both girls so we'll share. We hadn't seen each other in about a year and so were looking forward to spending some time together catching up.
She arrived late and wanted to go clubbing. We went out to a rock club where she proceeded to pick up some dodgy bloke and spend the night snogging him. He disappears and we're getting ready to go. Suddenly dodgy bloke appears again and will 'walk us home'. Get to the flat door, cue screaming tantrum about if I don't let them both in for a nightcap, she's going off with bloke, but she can't stay at his, so can I give them a key or she'll need to 'sleep in the park'
.
Knackered and totally fucked off by this point, I say fine to the nightcap and let them in. She then asks if I can sleep on my own living room floor and give her my bed as they want to have a shag
. I say no and he has to go, so she lets him out and I go to bed. She's staying up 'for a cuppa' and is 'pissed off with me' so will sleep on the couch.
Next morning flatmate stumbles over her and dodgy bloke (she'd obviously let him back in), naked on my living room floor, having pulled all the cushions off my settees. Dodgy bloke is given his marching orders and friend decides to leave a day early as we'd been unwelcoming. I thought maybe she was going off with bloke, but no, because he was 'just a random', 'not very good' and 'a bit weird wasn't he?'.
So off she fucks and I had to shampoo my carpet due to the suspicious stains jizz on my living room floor. 
I haven't seen her since. I shouldn't have been surprised, she had form for shagging anything that moved and in retrospect was one of those women who only need friends when they've not got a man, any man.