I’m assuming the worst they could figure out is what station was used at what time to do whatever I do.
Make sure those workstations don't have cameras nearby. Idk about the company you work for, but just because they don't have someone on staff that can follow your actions doesn't mean they're not willing to hire someone if they think they've been legit hacked.
They don't have to be line of sight, they just need to narrow it down to who is in the area. Don't underestimate boy's clubs willingness protecting their own.
Some remote shit/fucking around with printing something (like payroll) (again, ip and cameras). If email itself is publicly accessible, library, tor and fun
Trying to get them fired by sending things via their email will be tricky, since they can pretty plausibly claim they didn't send it. IT can pull logs, and even if they can't be used to identity you, they can demonstrate someone other than your boss sent the email. So, a mass email from their account won't do much. Especially if it's something out of character for them to send
Here's an alternative: If you have access to their communication and can find something bigoted they sent in private, you can forward that message out to the whole department. It was a real email and records will show they sent it, even if foul play was involved in exposing it.
If you have access to their email you can search for dirt that can be leaked to press. Check their browsing history for porn, that sort of stuff. If you can get their company credit card, order a sex toy from their workstation sent to their home. Go through their email and look for phishing/hacking attempts and get their computer infected, let someone else do the hard work.
Just be careful. Is there no wifi you can get into to make things a bit harder to track?
Death by a thousand cuts, comrade. Consider swapping some of their contact info around if there's some drama to be made there.
Fuck with their calendar, make him miss a meeting or deadline.
How about you stop talking about committing cybercrime on a website likely monitered by the FBI?
Whether you decide to directly fuck with him or not, definitely find a way to distribute the entire departments payroll anonymously. That will improve your working conditions in the long run, thereby fucking over your boss