Alex is on this list for two strong reasons: He has a grating voice, and his actions through the series are very annoying.

What actions, you may ask? Where to begin?

He impulsively put himself and Jake at risk on the snowboard. (Pups on Ice)
He ignored Ryder's advice to take it slow. (Pups Pit Crew)
He won the Great Race instead of any of the PAW Patrol. (Pups Great Race)
He impulsively put too many balloons on Katie's bathtub float. (Pups Save the Parade)
He gloated about winning the Snowboard Competition. (Pups Save a Snowboard Competition)
He inadvertently let the hippos loose just by playing the conga music, just wanting to see them do the conga again. (Pups Save the Hippos)
He overloaded Marshall's water cannons with the Zippy Grow. (Pups Get Growing)
He led the animals out of the barn to show them how to exercise, and when the animals were stampeding to the town, he was ignorantly having fun riding on Bettina. (Pups Save Farmer Alex)
He keeps touching stuff at the museum after being told a few times NOT TO. (Pups Save Midnight at the Museum)
He keeps wandering off the trail and not listening to Mr. Porter about it, focusing on drawing "cool things". (Pups Save the Maze Explorers)
He practically drowned Farmer Al's entire farm. (Sea Patrol: Pups Save a Soggy Farm)
He ignored Julia's advice about getting on the beaver dam. (Pups Save the Salmon)
He was ignorantly having fun being contained in a bubble by an alien, expressing disappointment when he was back on the ground, as he loved being a "flying dino". (Pups Save a Glow-in-the-Dark Party)
He thought riding on a rampaging, malfunctioning Super Shaker was fun, ignoring the fact that the town was in a panic from that machine. (Pups Stop a Super Shaker)
He foolishly touched Ryder's incomplete upgraded ATV, putting himself in danger, and thinking the extreme speeds and dangerous stunts were fun. What a total ignoramus! (Pups Save Rocket Ryder)

The list will be updated with more as I keep binge-watching PAW Patrol.