There are a thousand dumb ways for a criminal to rob a convenience store and 'using a palm tree as a weapon' has got to be the dumbest.
Not only will it not work, it could possibly get you killed. Why? Because convenience store clerks are hard as nails! Dealing with cheap customers and armed robbers every other day have made them into the special forces of the retail world. All the clerks I've ever bought a candy bar from smile about as much as Clint Eastwood. When they do manage to crack a smile they're also as scary as Clint, which is why I'm surprised this robber didn't get his head blown off.
And what kind of guy would think it's a good idea to rob a convenience store using a palm tree as a weapon? The same kind of guy that thinks it's OK for a grown man to wear a striped polo shirt during a robbery. Speaking of which, striped polo shirts shouldn't be worn by anyone over 10-years-old because it makes you look more like a "World of Warcraft" addict than an intimidating criminal.
Maybe that was his problem, he thought the palm tree would do +1 extra damage to any attack so he used it as a weapon. That or maybe he was just high. Whatever his deal was, he's definitely going to have to buy his Hot Pockets at another convenience store from now on.