"Your not that guy" is what you say when someone tries to act better than they really are and imitate someone. If they fail horribly, you tell them "Your not that guy".
Jim: Bro look im Steph Curry
*misses shot*
Bill: Your not that guy
Your not that guy but spicier with pal added to the end to it
Him: bro I’m going to fucking kill you
Me: your not that guy Him: I’m still going to fucking kill you
Me: your not that guy PAL
Him: woah woah woah take a chill pill I’ll back away I’m sorry dude