Most parties I attend are impromptu ones that are organized or just happen at close friend's places. They dont need to tell me, I go as I am, especially if it is very late in the day. It is also a Go as you are party, considering the state of people who attend it and have to go home. Many of them come as they are into the police station and spend the night there for drunken driving.
Other than that, yes, I have attended 4 of those, when I changed to something I want to be seen in not amounting to gladrags.

No

It happens here every second day!