Oh yes, this has happened to me!! My mom and I were at a restaurant for lunch one day with my son (4) and daughter (2.5) and it was fairly busy. A couple people in two separate booths next to us looked like they were having a working lunch. Both were on their phones, so I was extra sensitive to my kids' loud voices and actions. My son was able to get his act together after my redirection, but my daughter was just on a toot that day! I really like Jim Fay's choices, so that is usually how I begin to remedy the situation. I asked her if she would like to sit quietly in the booth or the car? She said booth and got quiet for about 30 seconds. Then she knocked over her drink and was still loud. I gathered up my keys, picked her up and took her to the car. I put her in her car seat and I sat in the front seat. I waited silently for a few minutes to calm down because I was annoyed with her and you can't talk (or shouldn't talk) to children with an emotional voice. Finally, I asked her if she knew why we were in the car. She told me because she was bad. I told her she wasn't bad, but I didn't like her behavior. I asked her what was she doing that I didn't like. She said being loud and not sitting down. I asked if she could sit still, be quiet and eat her food. She said she could, so we went back into the restaurant. She was very well behaved after that and when an elderly couple got up to leave that had been sitting directly behind us ,we apologized for being disruptive. My daughter said she got in trouble for being loud, but the elderly couple said she was doing a great job right then.
Tantrums will happen. The best thing to do is to stay calm with them and even though it seems like every single person is watching you, they aren't. I think people appreciate seeing a parent discipline their child in a positive way if they need to. Kids are kids and this is how they learn. Jim Fay's Love and Logic books have been a lifesaver to me as a parent and teacher. If you are looking for some great discipline strategies, they have great ideas. Go to www.loveandlogic.com for more information. They also have a great facebook page too.
HTH,
A.