...i'm finna laugh...

So earlier this year I witnessed two students talking in class.
They were trying to decide who would be the one to write for their group assignment.
After much debate, student one says "I'm finna do it!"
Student two, with haughty disgust responds by saying "Speak proper English man.  It's 'I'm gonna do it!'"
I wanted to intervene and make yet another correction.
Instead, I thought, I'm finna laugh.