If not basic decency, then at least self-interest -- given the possibilities that (1) you'll one day suddenly find that it'd strongly behoove you to kiss the ass of someone you once openly at-best patronized/dismissed and (2) they will not have forgotten it by then -- is a very good reason to behave well all the time.
In any case, I'm glad I'm more often under- than over-estimated. ("Better to underpromise & overdeliver...")