Yeah, the word "borrow" is only asking for trouble, so please no one request to borrow anyone's Pokemon.
I would recommend, also, that no one lend any of your Pokemon to others asking to use them. The ONLY situation where it would be okay to do that is if it's with your friend who you trust.
Mind you, we're not going to stop people from lending out their Pokemon, but it's at their own discretion. They're taking a risk when they're lending out Pokemon, and we're just simply warning you guys.
Threads asking to borrow Pokemon will, however, be locked or deleted.. especially those asking to borrow rare or high level Pokemon.