I tried playing versus for fun with my friend two weekends ago, the people we ended up playing with were some of the worst people I've ever played with (attitude-wise). I hadn't played versus for years and I hadn't even played the game in a while but these people were obviously really experienced and being dbags the entire time, but when the other random people on our team left some friends they knew joined out team and started team killing us and shit. The trolling was so over the top we didn't even care, I like jumping on to play a campaign every now and then but there seems to be a group of hardcore gamers who feel the need to ruin the game for everyone else.
I've put in over 500 hours between the two games (far more for the original), and you just summed up basically the problem with online gaming as a whole and why it will never replace single player.
With a good group of people, or with friends, it's phenomenal. With a few dicks and douchebags, your night is ruined. Often times, as adults, that might be one of your only free nights to game.
My favorite would be the people who would join, immediately change their name to another member's STEAM name (to make it harder to kick them), then blare racist music over the mic while teamkilling everyone. Or even better, the ones who would play normally up until the group nearly reaches the safe room, then do all the things I just mentioned.