Couple years ago I definitely learned a lesson about caddies - we were playing a tournament at Pinehurst on #2 and I thought, hey, why not get a caddie for myself and if the other guys on my team don't want one no big deal. More of a money thing for them. Plus a couple years before that we got a great caddie so I wasn't really thinking about potential negatives.
They give us this guy who was like the perfect stereotype of grouchy old man. Plus he couldn't carry my bag, so he got a cart. You'd think his age might be an advantage in experience, but he couldn't read greens for shit. He also had old-timer yardages in his head and kept picking clubs for me. None of which would have been THAT bad except that he loved to argue everything. Typical exchange.
"Hit this 6 iron."
"What's the yardage to the front?"
"I said hit the 6 iron so go on and hit it."
"Ok what's the yardage to the pin?"
[ silence ]
"Seriously what's the yardage?"
"... 130 yards to get on and 140 yards to the pin."
[ I grab PW ]
"You can't get on with that club!"
[ I hit it maybe 15 feet, just short and beneath the hole ]
"I TOLD YOU YOU CAN'T GET THERE WITH NO WEDGE!!!"
Any disagreement was pretty much a Tunnels-style argument where he'd find some way to be right even if I hit a good shot. He tried giving a read to another guy on my team who is a really excellent player - he ignored him and it broke the opposite way the caddie suggested and lipped out. Said he hooked his putts and it makes them break the wrong way. Next hole he's raking a bunker and my same guy grabs the stick to tend it. Our guy is about to pull the trigger on his putt and the caddie yells to drop that flag stick because that's his job!
In hindsight I should have asked him to just leave - definitely killed our team's attitude and pretty much trashed the experience in general. Needless to say we didn't play that well.