Not half as rude as an out of control kid having a meltdown or wrecking their house.
Well yes, of course, which is why i said it's better not to go visiting. I don't want to derail about my dc ( but in brief answers to your questions i have seen supernanny and have one of her books along with many many others - nothing works and as for the asd rule book, my ds hasn't read it and in actual fact loves surprises and gets much worse behaved if he is 'prepared in advance' 
He appears to have heavy aspects of pda and is 'self led', so no amount of preparation makes any difference. You should see him in the drs surgery - last time he ripped down the curtains and 3 of the shelves :( curtains, throws, soft furnishings and cushions excite him to the point he can't control himself).
However, my point really is it's irrelevant why your dc cannot behave, it is still miserable for them to be told no constantly and told off, it's really miserable you to have to do it and i'm sure it's monumentally miserable if you are being the one visited. I know people without dc (or who had extremely compliant/quiet ones) who do really expect them just to sit quietly with little or no interaction and get pissed off if anyone has to give them attention when they feel that they are the one being visited. Which makes trying to entertain your dc really really hard.
My dad gets cross and say's 'I'M TALKING TO YOU' if me or my mum gives dc attention when he thinks it should be on him - but sadly 2 year olds don't wait for opportune moments to yank open a drawer or tip up the water bowl. He also believes i should just be able to tell them to sit still and they should, with no toys or anything else.
Anyway - my point is, without all the waffling, that you probably just shouldn't go, it doesn't sound like anyone gets anything out of these visits.