Bow your head an loudly pray to Odin for strength in battle and the power to smite your enemies. Smile and walk away.

That's a very British response and I feel for you. Perhaps some American-style pentecostals have taken up near you? If so, please accept my apologies as an American for yet another of our unsavory exports.

I like @jeshuey's idea of quoting Matthew 6:5 in response best of all the prior responses.

As a former Pentecostal I'm very much aware of it and I think people do it for attention. I detest it. Today I'm at the point where if others pray over a meal I'm looking around to see who else might be looking around. If you find one that might be your friend. I'm almost at the point of starting to eat anyway and ignore all those who are praying.If they protest tell them they should thank a farmer.

Point them in the direction of the nearest church.

I “pray” out loud when I’m at the gym and I don’t want to hear other people’s loud conversations or the TV is annoying me.

Do not hesitate to point out to such folks Jesus' words in Matthew 6:5 -- "And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward."

I live in the Bible Belt and have come across this in a private community pool. I've been asked if I want to pray with them. I say "no" and just continue to enjoy my pool time. They're not screaming so it just sounds like chatter to me. I have never experienced any thing like that in 52 years in New England.

I've been seeing it for ages. It always makes me really uncomfortable.

I live in the bible belt here in the U.S. and see this quite often when I go out to eat. I ignore them.