Being specific is hard because it's just a category of being a bad partner, and as such there's plenty of ways to do it lol.

I'll start by giving a quick overview on how to be a good kink partner: respect boundaries and know your own, communicate and listen, build skills appropriate for your role and interests (you can learn more by talking to people into that interest in the community, especially in the other role, and learning both sides even if you only want to do one is encouraged), know what you want and don't want, but be open to what you're not sure about, and in general just try to see everyone in the community as full people, not just as [role]. And for that last one, I really can't emphasize enough how much better you come off if you have friends across roles and genders, but also the people you're compatible with are just people, don't put them into their role until you've discussed it and agreed to it.

A lot of the worst experiences involve people who have personality disorders that aren't sufficiently dealt with for relationships to be a good idea. All of the really bad subs I was thinking of in my comment had borderline personality disorder and had not undergone dbt. They were all also kinda looking for a partner to fix them. But also the domme that got pushed away had bpd, but had underwent years of treatment and had developed healthy habits and understanding of her limits.

So for some specific bad behaviors. Boundary pushing is big. If someone says no or gives an excuse, that means no unless clearly negotiated with a safeword to replace the no. Attempting to negotiate someone's boundaries or to guilt them into something they're not interested in is very bad. Overdependance on someone is bad, especially when they don't agree to it. Your dominant (or submissive) isn't your therapist they're somewhere between romantic partner and fuckbuddy, and you should know where you stand (if you don't know, talk about it with them).

Now for just general bad form things, they're more akin to being a bad lay. Dominants being overconfident and doing things they aren't skilled enough to do without giving a heads up (plenty of experienced subs will agree to be a practice dummy to someone they trust, but it's often not cool to try something the first time without saying so). Subs that come in with a checklist of things they expect from a scene rather than presenting a menu of options and limits and letting the dom construct a scene out of it. Related are the subs who can't let go of control in a scene after asserting that that's what they want (if you say it's what you want but you're unsure you're able that's a different story). The inverse also sucks, subs who don't know what they're interested in or what their limits are (and "no limits" is neither true nor appreciated). Subs who neither have skills nor interest in building them. People who jump right into roles without talking about it.

In general new people are given a lot of grace and so long as it's not overt consent violations the worst a new person will need to do is apologize when corrected and try to do better.