Showing up by yourself to this event isn't ideal, so you've invited your friend or roommate or date. Beforehand, you totally overdo the precautionary warnings ("Now don't be mad at me if it's really lame," "It's entirely possible like only two people from my office I know will be there"). "I'll be fine!" your friend persists and suddenly you feel like a parent taking their unhappy child to a family friend's house for a long dinner party or something.
The whole time you're at the bar you're anxious that your friend might be feeling bored or uncomfortable. You're talking with your coworkers but you keep contextualizing everything for your friend so he's not lost ("This woman seriously wears the exact same cardigan every day"). And when each conversation ends, you get paranoid and weird and whisper some sort of excuse to your friend ("I think Mark was kind of tired tonight," "Kate doesn't usually talk about her boyfriend so much") and your friend will say something like "No, she seemed really nice!" and you think about how you don't even really like Kate and now you're ready to leave the party even though you've only been there for like ten minutes.
You go to the bathroom and return to find your friend talking to the one coworker who always acts sort of weird to you and you don't want to go over to them because then it's like you're relying on your friend to survive socially at your thing, so instead you read old texts on your phone for a minute and finally, left with no other options, you uncomfortably insert yourself in a conversation Kate is having with some guy wearing a scarf.