LOL! I've had managers who said "You can be replaced!"
I had an office manager years ago who told me I needed to improve my attitude and said if I worked in the main branch I would've been let go a long time prior (I had a great skillset that would've been difficult to find from anyone else at the rate they paid). Granted, she might've been right about the attitude, but her threat really didn't help. Anyway, the person (who I actually liked and did have the "can-do" attitude she was mandating from me) who she was comparing me to was a temp who got hired in the main branch shortly thereafter...and was fired a few months after that (guess that can-do attitude didn't work for him either).
Not too long later, Office Mgr hired a second assistant because the workload I was handling solo had greatly increased. Office Mgr said she was hiring based on personality because anyone could be taught to do what I do but that it was hard to find a good personality. I'm really not surprised that the brokers 2nd Admin supported were really frustrated because she didn't know how to do anything (a 20-something recent college graduate who didn't even know how to use the tab key in Word, rather than using the spacebar -- this was 2002 so not that long ago and not unreasonable that she should've known how to use a computer reasonably well). 2nd Admin didn't last very long either but, fortunately for her, she resigned of her own volition (nice girl but really had no business doing computer-based tasks).
FINALLY, glory came after 3-4 years of Office Mgr's snarking at me and unreasonable requests (like demanding in my annual evaluation that I get a local physician, rather than the one I was still seeing two hours away -- I pointed out and, I believe, wrote as a response in my evaluation, that I used my vacation time for my out-of-area medical appointments so she could not dictate to me how to use my vacation time...yeah, she backed down on that one, among others). She didn't listen to her own advice so rather than get the licensing for herself requested by one of the major brokers in our office, he got her booted from our office as Office Mgr. She was transferred to the main branch but, because she lost about 2/3 of what her job duties were (1/3 was event planning) but was still getting paid a huge salary, she got "laid off." I wonder if anyone told her, "You can be replaced" (because she sure was and with someone who had more years of experience in event planning).
The best part? After I resigned (on good terms -- I moved away), I still maintained contact with my old office (they were my job references). I learned from the broker manager that it took three attempts to finally find someone who could sufficiently replace me (meaning they hired three different individuals before finally finding someone who could do what I did).