Find That Book

There is this one book that I've been looking for for years, my intermediate school teacher would read us a new short story when we had enough time. I know it's an old sci-fi book, it could have been published any where between 1950's to 1990's. It's a book full of short stories, but I only remember one small scene of a story. It's set in a diner, a human man is looking at human-looking alien strangers that just walked in the diner. The strangers sat down, but the strange man didn't pull his pants at the knee to sit, and the human man watching that thought that was odd, because every male knows to do that, so their slacks don't bunch and tighten.

That's the only part of the whole book I can clearly remember, though I think there was another story about robots being used in homes. Sorry this is all super vague. I hope someone, somewhere can help me