Also be careful to avoid ad hominem attacks.
In other words "Play the ball, not the man."
It's fine to disagree with someone's posts or opinion, e.g. "Your video isn't very good." or "Your post makes no sense." as the object of these statements is not the person themselves but the "video" or the "post". However, when you begin a sentence with "You", you're making the person the object of the statement, and when it's followed by perceived abuse, such as "suck" or "are an idiot", you've crossed the line into abusive behaviour.
Please take note of this and take care to distinguish between the 2 cases in future, the former is fine, the latter isn't.