Thanks for the positive response.
I’ve found that people who consistently appear rude on social media are genuinely unpleasant people.
Social media distances us from the person we’re speaking to, and (almost) places everyone on the same level—there are fewer cultural, social or practical gatekeepers in the way of you talking to your Hollywood hero on social media, than in real life.
However, for some, social media dehumanises people they communicate with—trolls and harassers are all too frequent extreme cases of this. To these people, being rude to people on social media is permissible, if not outright acceptable and enjoyable.
While such people may never be rude to another person in real life, or they may view their social media persona as a bit of fun, that they think such behaviour is acceptable at all, in any venue, let alone a professional one, reveals a vicious nature.
But this is where “stalking” comes in: if the person’s initial contact with you seems rude, and it’s an outlier compared to other posts, it could well be unintentional (as you say, they may be distracted from having a bad day). But you feel they are rude to other people as well, I advise avoiding them.
Practising at events you are less invested in is a good idea. Events that get listed at Meetup.com may be good for that.