So my uncle's pretty awesome, but my family is pretty much ESL and some idioms fly below their radar. My uncle, in particular, demonstrates how wrong this can go. He really wants to use a particular idiom, but keeps screwing it up, and that slight difference changes the meaning drastically.
He really wants to say "I'm pooped" when he's exhausted.
But he registers the suffix of "-ed" as past tense and changes it to what he feels is present tense.
So in the middle of a conversation he'll just sigh and say "I'm pooping."
From a pretty butch middle aged man this is always pretty surprising. I've tried to explain why it's wrong but he doesn't