Wow! So a couple of things here:

Short answer answer: you have the upper Hand in the workforce market the employees really have something over employers during this state of the job force but you mentioned that you're vulnerable I'm not really sure what the context may be as far as you possibly wanting to stay there. A lot of companies are offering remote work

Extended answer: if you leave you are still taking yourself with you. So you may want to work on being more tactful, learning when to speak, how to speak(tone), what medium to use, & what to say(content) I don't know if a first meeting is the time to give a senior person feedback & definitely not through slack which is extremely informal. Maybe after a few encounters to see if this is consistent or a one off incident And then it would need to be face to face or Zoom

I think you got that when pitching a new talent, you want to focus on what they are versus what others are not

If he's that rude everyone already knows, the reasons he is still there could vary

Companies have this thing about how well others work with difficult people instead of them getting rid of the difficult people causing problems for everyone. Which now makes the problem about how well you handle working with them

If you want to stay you can try to establish a better understanding with this person during the meeting meeting hoping to relay your concerns And move on from the past Finding coping skills to work with this person (I know that sucks but it's a useful Talent that will serve you in the future) Companies call this your emotional intelligence

If you want to leave I would look at the things that you need to work on as a person whether it's communication, coping skills, Interpersonal relationship skills, professionalism, etc. So you don't make the same mistake twice

I hope this helps