This "mysterious third verse" is sung on Garth Brooks' live album after the regular two verses and choruses

Well, I guess I was wrong
I just don't belong
But then, I've been there before
Everything's allright
I'll just say good night
And I'll show myself to the door
Hey, I didn't mean
To cause a big scene
Just wait till I've finished this glass
Then, sweet little lady, I'll head back to the bar
And you can kiss my ass

Chorus:
'Cause I got friends in low places
Where the whiskey drowns and the beer chases my blues away
And I'll be okay
Well, I'm not big on social graces
Think I'll slip on down to the oasis
Oh, I got friends in low places