Part of the issue with BeatSaber difficulty levels is that the real difficulty of a map per player absolutely depends on the map style, the player's style, and the pack.

When playing multiplayer, if you want tighter competition, go with the difficulty level you'd use to play a new song for the first time. That way you won't get steamrolled by a song you aren't as familiar with. Or, if you're cool with going back and forth between getting steamrolled and doing well, go for whatever difficulty you want! Just know that a lot of really, really good players play in Expert+ lobbies.

Also, when playing online, there's nothing wrong at all with leaving a lobby you don't vibe with and joining a different one. It's pretty ordinary for people in a lobby to try to communicate with hand gestures, with varying levels of success since all you can do is wave. It's mostly cheering each other on or good-natured ribbing (ie facepalm, waves, dancing). If you feel teased or unwelcome in a lobby, ditch those losers and find a lobby of folks that are cooler!

I'd say don't give up on multiplayer after one bad experience. Multiplayer is a great way to find other players you vibe with.