I've started a job in a small company a few months ago, I really like the role but there's a colleague who's been here a few more months than I have that I work with whom I have been experiencing some difficulties with.
While I'm presenting in our weekly strategy meetings, this co-worker constantly chimes in with ideas that aren't fully relevant or will then try to summarize what I said after I said it and poorly. I've also noticed that when I talk with the CTO and they assign me tasks, this co-worker tends to verbatim say what the CTO said, which I find annoying and inappropriate and they aren't my superior.
Another problem: I was assigned to validate the performance of something they wrote. I tested it and found that it had performance below what my colleague had claimed. They offered thousands of reasons why my assessment was wrong, I went ahead and decided to indulge them here by going through my assessment and seeing if they had a point. They claimed they had extensive tests for the module. I informed everyone involved that I would continue with evaluation and begin building a better module unless they would supply me with their assessment data, code, setup, etc, etc. I ended up finishing the new module as they never actually provided any of the asked for resources above.
What is this behavior? How exactly do I proceed and how do I bring this up to superiors, or even how do I have an effective conversation with my colleague here?