For me, it's the complete and total inability to focus on anything without caffeine. I can't even do something I enjoy for longer than 10 minutes before I'm off the rails doing something completely unrelated for 2 minutes before I'm on to something else unrelated for another 2, never getting back to the original task.

Having a fixation on a hobby for me, instead of meaning dedicating myself to it, means thinking about it constantly in between goofing off, and never being able to actually get myself to do it, to my own immense frustration.

Writing is probably my biggest fixation I have, and I have dozens of 40 page long plot skeletons for series I want to write, all written a single paragraph at a time per day, and exactly one novel where the first draft is half finished after 3 years of work, and I haven't written a single word in about a year because every time I sit down to write, I literally immediately get distracted. Forcing myself to do it in various ways instead of goofing off results in feeling horrible, and writing horrible quality writing I have to delete the next day, all because my brain could not engage with what I was doing, even though I absolutely love it normally.

And the biggest indicator that I have adhd, besides being actually diagnosed with it, is that all these issues vanish when I drink absurd amounts of caffeine. I can write and enjoy it. In fact, I can write 10,000 words in a single day and absolutely love every minute of it. Albiet, it tends to be 10,000 words into a novella I end up trashing, but that's still productivity.

As for autism, well, I have difficulty communicating, can't talk to somebody about anything without looping the conversation around to me (how do you even talk without talking about yourself? Still can't figure that out,) and also have extreme sensory issues. If my hands are even slightly dry I retch, if my fingernails are too short, same thing. I also can't be around large groups of people because it overstimulates me immediately and I forget how to everything.