Oh, I agreed with that first one on 'artist who seem to spend way too much time on the internet"
My personal pet peeve would be artists who take on loads and loads of commissions, feel stressed by their workload, and end up not drawing what their clients wanted in a timely fashion without multiple messages or simply disappear with the money without a refund. Then they would pop back up again, and open more commissions, only to repeat the process of
1) I'm dying under my to-do list of commissions
2) opens more commissions slots
3) people don't get their commissions done or it takes more than a year to finish
4) refuse refunds / pretend it never happened.
Please don't be the cause of your own stress: don't take on my work than you can handle, and communicate properly with your customers if you are unable to get their commission done in a timely manner.
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The other one pet peeve is yeah, the call-out culture. I've had a friend of mine from Deviantart go to the farthest ends to try and claim that one artist stole design ideas and was a tracer. Some of the overlays to prove that something was traced was just barely credible. I don't think anyone, even if they did trace, deserves to be attacked by another artist and their legion of friends/fans and have their reputations smeared enough that the delete themselves from the community. This isn't positive behaviour.