I have ASD with sensory processing disorder in addition to my ADHD so I have always assumed my social fatigue derived from that and not the ADHD but I suppose it could be ADHD related as well. I do know that my social fatigue has less to do with the kind of people they are … i.e. happy/positive vs. self involved/selfish/negative … and more to do with the number of them and my relationship to them.
When I am someplace with a lot of people, like a restaurant or a party, I can not really hear anything. Someone sitting right next to me could talk to me and it is only slightly easier to make out than the person across the room telling their kid to stop picking at their food. I hear everything at the same level and so its all just kind of overlaid into a buzzy painful mess. Sometimes it even interferes with my ability to hear my own thoughts. So any amount of time in that kind of environment is very tiring because I am spending so much time trying to make out what other people are doing/saying.
The other issue for me relates to relationship with the person. I find strangers to be more tiring than people I know well. I think this is because I am spending a lot of my time trying to ‘act normal’ and hide my ASD, as well as figure out what the strangers mean when they say things or when they are being sarcastic or serious, etc. Someone I’m close to is less tiring because I already know their patterns and so I’m expending less energy trying to read them. People I ‘know’ but have not been around in a long time … like family that I see once a year … can be just as difficult and tiring as someone I have never met before. The one exception seems to be strangers who have similar patterns to people I already know. A stranger like this who is easy for me to understand/read can actually be exciting and I’m prone to interacting with them for hours without fatigue.