Discipline in Public

Its not rare for my children to embarrass me when we are in public, especially since Luke has discovered toilet humor. We can usually just brush it off, because its in front of strangers. But Sunday was different. We had planned a day out at the zoo and were getting ready to leave when Clint's brother called and asked if we wanted to go out for lunch. We always enjoy their company, so we agreed. We met them at one of favorite restaurants on Cherry Street, and from the moment our boys saw theirs, they were set on Attention-Getting mode. When we are in situations like that, I have no idea what to do! They never act like that at home or at school! I tried being calm, but eventually stooped to empty threats to try to get them to act right. I have never been so humiliated as I was yesterday. I'm now searching the internet for alternative discipline methods for in public, but any suggestions are welcome!