system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is actually going on in the brain to make people feel bad in uncomfortable social situations and how do these responses develop?
gpt
We have a part of our brain which is designed to keep us safe. This automatically makes us want to run away if we might get hurt in a dangerous situation, or to stand up for yourself if you can fight. This is very helpful to keep us alive, however there can be some social situations (when we are around other people) where this part of the brain gets a little bit activated, making us want to get away, or we get nervous jitters or we want to lash out in defence. The brain is getting you ready to run or fight, if needed. That happens often when we interpret the situation to be very uncomfortable or awkward, as well as when we think the other person(s) are very important compared to your self-worth or there is something the other person(s) are doing that is dominating, aggressive or sexually undesirable. 

These reactions develop based on the way the situation "occurs" to you. There are some people who it mentally occurs for them that they are in a threatening situation in most social situations (so the fight or flight reaction activates) yet with other people the exact same social situation occurs as something they can easily handle, so the reaction does not activate in the brain.

The idea of "feeling bad" which OP asked about is our interpretation of what we are experiencing in the nervous system as well as mental judgements about our own value/social status/self-worth.