"Non-Senior" engineers who have to pretty much mentor "Senior" engineers; the "Senior" being given the title due to X years of experience instead of actual knowledge and knowhow and of course the reverse where the "Non-Senior" does not get promoted because he does not have the required ~years of experience~.

I see it more rarely amongst higher job titles though. It's more difficult for a senior engineer to make it to lead or principal when they do not have the skills.