I had HORRIBLE service one time at a Denny's in NJ in the mid 90's. We had 13 people. Was made to wait almost an hour for a table. And right before we were seated another large group of people came in and were seated before us. Our food was late & cold. And we were afraid to send it back because we were SURE we would have had the food tampered with and sent back.
I took a penny put it under my coffee cup, in the saucer. We never went back to that Denny's. And since there was a gaming convention in that town twice a year we told all of our friends to boycott it too.