"Oh... It's you... thought it was people. Bye."
Or if you really wanna fuck with them let them in, lock the door, then start getting creepy. If you have a gun, just start cleaning it very carefully in front of them while listening to them, if you don't get a big knife and just say something like "sorry, I hope it doesn't creep you out, it's just a nervous reflex". Pretend to be interested but once in a while ask stuff like "say... How tall are you again?...6 foot 2? mhh... Ok, in three pieces, that's slightly over 2 ft a piece... it's ok, I can do that... Sorry, go on". Make sure you have a very intense expression on your face.
If they're being persistent then get REALLY in their faces about it... "So... like... hypothetically... Like, just saying you know, but... hypothetically speaking... what's your church's view on... and I'm just putting it out there you know, hypothetically... Murdering hookers and eating their livers...? Nono! I'm just asking! No reason, I just... Just thought of it, sorry.". Then let them go on and keep popping up shit like that. "What if it's an 8 year old child instead? Just saying. No reason.". Maybe get up, go to the window and start closing the blinders, looking outside suspiciously and shit. Ask them shit like "Say... How fast can you run again? Sorry, just, small talk! But would you say...olympic level? No reason.".
If they last more than an hour without trampling each other to leave, you're doing it wrong. And when they do, before you unlock the door, make sure you deliver the final blow "So soon?! But I didn't have time to show you my basement... Sigh... Ok I guess, but do come back some day ok? I wanna hear more."