Here's the deal ... Jesse's pet monkey, Tobi James, got loose, slipped into a neighbor's pad this week, and then things got super wild. Tobi ran around the house, knocking over cups of coffee, climbing up and down the stairs -- and, obviously, REALLY excited about it.

Yep, adolescent monkeys get boners too, and Tobi was sporting it his during his hijinks ... as you can see in this video.

Jesse's neighbor, Carrie, tells us Tobi barged in Tuesday around 8:30 AM, when she heard what sounded like someone trying to break in. She says she saw the door handle jiggling and got the creeps -- but still decided to slowly open the door.

When she did, the little critter dashed inside and started monkeying around. Yes, that's a euphemism for playing with himself ... all over the house!!!

Carrie smartly consulted a Facebook page for her town of Dripping Springs, TX -- and folks there told her Tobi belonged to Jesse, who came over to pick him up.

Carrie says Jesse was apologetic and explained Tobi is about 4 years old, which is like a teen in human years, and y'know what that means -- puberty and hormones. Jesse thinks that's why Tobi bolted from his house.

We're seeing a lot of cold showers in this monkey's future.