BG: The friend is an ex boyfriend who I dated about 10 years ago. Very ex, no interest on my part of dating him again. I'm going to refer to him as "my friend" in this post because the relationship was so very long ago and relatively short.
Some months ago, my friend had said he was coming to this area on a combination business trip/vacation and I offered my place up for him to stay for the weekend - I was between spring and summer semesters at school, and I could take that weekend off of work with no penalty to spend time with him. Some things came up at his work and he ended up not traveling down here. Fine by me, it was sufficient notice, didn't leave me out any money (I hadn't bought groceries/supplies for hosting nor had I purchased tickets to anything, etc.) /bg.
My friend was supposed to travel down here next month for a convention in a nearby city (I live in an area where several major cities are within a short drive of each other, I live in one, convention was in another.) He was going to come over to MY city for a visit to the attractions in my area and to hang out with me. He decided a few days ago to change his plans and go on an actual vacation in my city instead of going to the convention (his employers would have expected him to do SOME work at it, as it is a fun convention but in a field related to his work.) He asked me if he could "crash on my couch." Now, in the intervening time since the original offer to allow him to do so was made, I realized that he does still seem to have a great deal of...interest...in me. I'm emphatically NOT interested in him. He's aware of that. I am therefore not entirely comfortable having him stay in my house with me, not to mention several other factors unrelated to him that would make me reluctant to have ANY guest in my home at this point. The conversation went like this (this is actually a copy of my log of the conversation, names redacted. Apologies for the poor spelling and lack of proper capitalization and punctuation.
him: also was wondering if i could crash on the couch?
me: my couch really isn't an option
him: i got an aero bed
me: yeah my place just isn't good for a stay
him: oh ok
At that point, he gave up asking and I offered him a brief explanation of one of the other factors that made him staying with me simply not feasible. But go e-hell - I avoided having to offer excuses that could have been overcome (which the first attempt at it inadvertently ended up being because I echoed his phrasing and just said my couch wasn't an option...oops.) But it worked! Now to use it on the significantly more etiquette-challenged...