It's never a good move to make your boss feel dumb.
Also, some people with low self-esteem try to sound smart by using fancy words. It's often easy to notice.
There are exceptions, where some people (e.g. Russel Brand, Stephen Fry) use lots of obscure words to great effect.
@Cleisthenes @jcbrand doesn't even need to be your boss, know your audience and if you can say it simply intelligent people will respect that also