Kirk Gibson: I Gotta Nickname For My Parkinson's ... 'I'm Not Gonna Give In'

Kirk Gibson is an absolute badass ... telling TMZ Sports his Parkinson's disease is a huge pain in the ass -- but he REFUSES to give in.

The MLB legend was at LAX when he started talking about "this guy I carry around ... his name's Parky."

Our photog didn't quite get the connection -- but it's clear Gibson's talking about his medical condition, which he was diagnosed with last year.

You gotta watch the clip ... Gibson keeps it about as real as it gets.