I've worked a lot of jobs with a lot of people who don't know what marginal rate means. The most common way I can tell is when they say they don't want to work OT because it will cause them to go into the next tax bracket and earn less overall. You should be able to explain why that's not the case, but then keep quiet cause it tends to lead to arguments at the workplace ;)
Good Lord, you worked with *all* my uncles? :-)
