Can you get a video of it? I’m interested in this phenomenon for research purposes.
Edit: I have just been informed by my editor that this would be “unethical” and that she knows that “all [I] want to do with it is be endlessly entertained by a chatot that swears like a Unovan sailor,” so allow me to answer this question properly.
That having been said, some people like to employ the use of scarecrows to ward off any kind of bird pokémon, so this may work for your visiting chatot as well. Your scarecrow can be a traditional one or any object (handmade or store bought) that resembles large, imposing predators.
Alternatively, hang large (but lightweight) or reflective objects in your trees. Make sure they’re capable of turning with the breeze, and set reflective objects up so that they shine light either into your garden or into any possible flight path of this chatot. The amount of movement both the objects themselves and the reflected light from the shiny ones can confuse chatot and make them think that something is prowling in the garden. This in turn will drive them to avoid landing, as they’ll consider it unsafe.
(As a note to the above, some gardening stores sell holographic bird pokémon tape or hanging disks for this express purpose. It’s cheap, lightweight, and virtually harmless to your trees. I would recommend the disks, as they’re less likely to blow away in higher winds.)
Sounds can be used to the same effect. Planting a speaker that plays glameow and purugly calls may drive your visitor away by making it think one is lurking about your garden. If you can’t afford an outdoor sound system just for this, hanging empty tin cans in your trees works just as well, as the loud rattling they make can annoy a chatot to its wit’s end.
Then there is, of course, removing anything the chatot may perch on. Coating artificial perches (sculptures, for example) with something slippery but environmentally friendly (such as cooking oil) can discourage this chatot from landing, as it won’t be able to get a good grip on the thing it wishes to rest on. Some gardeners also use bird spikes to discouraging perching. Despite their rather garish appearance, bird spikes are typically designed to be dull enough that should a bird pokémon attempt to land on them, they’ll only be made to feel uncomfortable, rather than stabbed repeatedly. Nonetheless, I’m personally hesitant to recommend these, as, well, they are literally spikes you use to discourage birds from landing in your garden.
Finally, should none of the above methods work, obtain a glameow or purugly (or even a staraptor) and train them to chase away the chatot whenever it comes close.
Alternatively, if all of the above methods fail—even the last one—catch the chatot and teach it something a little less inappropriate.