A Slayer with two 1-Hand Axes equipped, using Natural Bond and no Curse Resistance. Although that would be fun to follow in a stream, bonus points for soloing.
On a more serious note (and once again a reminder, I don’t generally play publicly), none of the careers (or weapons) are bad enough to warrant dislike just based on it. Some things certainly require more skill to use, but you cannot judge a player’s skills on their equipment (or even character level) alone. A bad Ironbreaker will still go down, and a good WHC can tackle maps with taking hardly a scratch.
In general, I’m not even sure what kind of setups I would be most wary about. Probably ones using what the meta considers “mid-tier” weapons. The strongest setups can generally do something even with average skills, and the weird setups are more likely to be someone skilled trying out something fun.
If I had to choose something beyond obvious jokes (like my opening setup), I guess BW with Beam or Bolt staff could be the one. Those staffs on BW are a sign that the player isn’t really utilizing the career’s capability of fast charges of strong spells, especially Beam, and Beam is still the most versatile of Sienna’s staffs, and (as I see it) still considered the pick most strongly following meta (which suggests someone who doesn’t know basics of the game well, and relies on raw power to carry them ahead).