As a ralts and kirlia and early stages of Gallade, Psythe was very shy and timid, to the point where other Pokémon would pick in him. but now that he’s learned low kick and psycho cut he’s become a lot more aggressive, even to his own team mates. How can I curb this bad behavior?

Simple, anonymous. As his trainer, it’s up to you to teach him not only techniques but also discipline. Teach him that there are times and places to use his attacks and that, outside of a battle under your command, his attacks are only to be used against another pokémon only as a last resort. Provide him with other outlets to relieve stress and anger, and be sure that you’ve trained the rest of your team to treat him like, well, a teammate (that is, someone to help when they ask for it).

Best of luck, anonymous!