Thanks for arguing my side, Onyx - I had to go before I could address David's question last night.
It is highly unusual for anybody to point out that they are on a break while using Apparatus (or any other thing, for that matter). For one, it is very clear that it is in use because it is on, and there are things scattered around in it.
Second, it is in the interest of someone wanting to use Apparatus to inquire if it is free.
However, Barney has shown that our regular practices don't apply to him so I went out of my way and somewhat sarcastically pointed out that I was still working, despite it being blatantly obvious.
What I expected is "I understand I was wrong yesterday.I won't do that again" Or at least a normal human facial expression expressing contriteness or shame. I know if a senior member of my lab had said something to me like that after having screwed up, I would be completely red-faced. (Exactly what you wrote, Mental Magpie)
Instead, he acted as if I was doing him a courtesy.
It's not as if I expected an "I'm so sorry I put you, your fetus and every other person in the lab at risk."
David, Barney was there. He knew exactly what happened. He didn't need the context of my OP.
There was no miscommunication. I asked him if he knew I was working, he replied "yes", then tried to blame Maddie.
If he had asked "why are you telling me this?" - it doesn't necessarily have to be snarky - I would have replied "because your actions yesterday demonstrate that you don't know the proper lab protocol for shared equipment."
FWIW, the whiteboard sign-up for apparatus is right next to Apparatus.
When I mentor a new student, I explain what we are doing, then detail the hazards we may be working with. I explain the precautions we will take and why we take them. My method is usually "You watch me do this once (or as many times as you need), I watch you do it once - or as many times as you need until you feel confident enough to do things independently. Then, I will be in the area for any and all questions you may have"