Years ago I was on a business trip in Colorado. Had a pretty decent expense account.
Went to a teppanyaki restaurant near the office. Not a place one usually goes by yourself, but I wanted something different. They seated me at a table, then shortly they seated a party of 6 senior citizens at the rest of the table. As I was sipping some tea, they asked
"Do you served an American food here", and when the puzzled waiter said no, they all got up and left.
I ended up at a table by myself for the evening.
Another occasion where I wasn't present but my wife was. She was having a meal with a few other ladies, and a group of men sat at the table next to them. Turns out they were a manufacturer and several dealers that I regularly buy stuff from. The manufacturer was telling his dealers about a coming price cut, to react to expected market competition. For the next few months the dealers were having "crazy" sales, dumping inventory before the retail price on the merchandise dropped to what the wholesale price had been. But thanks to what she heard I passed on all the sales, and waited until the price cuts that followed.
And not a restaurant, but I was on a train one day, in a car wilt a lawyer on his cell phone. He was babbling non stop loud enough for everyone to hear, what I could only describe as privileged client communications. I really wish I had known who the client was, so I could have called them and told them how stupid their lawyer was.