Hello Zulubump!
I'm not on MN much these days but I am training to be a C of E vicar and have done some work on the letter of James, which I personally love! I wonder if a little bit of background might help...
James is often described as a Christian-Jewish wisdom book - there's a lot in there about wisdom (like, 'if any of you lacks wisdom, you shuold ask God who gives generously'). Like the Hebrew (Old Testament) wisdom books, like Proverbs, there's an emphasis on wisdom being shown by what you say. Proverbs has got loads of interesting things about speech in there - one of the strongest statements being that 'the tongue has power of life and death', which is obvoiusly, literally true in cultures with the death penalty. It's still true, but less obviously, all the time. You just have to think of some of the awful stories about bullying to know how true this is.
So James is standing in this wisdom tradition, and using pretty similar language to Proverbs to talk about the power of speech. With all respect to your lay preacher, I think it's not so much about saying OMG but it's more to do with the big issue in James' letter, which basicall ycomes down to 'You call yourself a Christian? Show it by the way you treat other people'. One of my favourite verses in James says 'do you with your acts of favouritism really believe in the Lord Jesus Christ of glory?' I love James because it's all about living out Christian faith in community, by loving and serving each other regardless of status or wealth. So I think that the stuff about the devastating effects of speech is about Christians speaking badly of each other and failing to love each other.
As someone who's pretty much always been a member of the church, I hate it so much when people gossip, and bitch about each other behind people's backs. It makes me really angry tbh, and I'm glad that there's a Biblical writer who's angry about it too. It hooks into the theme in Paul's letters about being the 'body of Christ'; if we really understand that we are the body of Christ, and individually are members of it, we start to see that bitching about someone else in your church is so destructive not only to them but to the whole community, ourselves included. There's one line in the letter to the Galatians where Paul says 'If you're going to bite each other, take care tht you don't end up devouring each other' and I think that's much the same thing that James is getting at.
I love talking about the Bible so if you have anything ele you want to talk about, do post!