That was a joke. Let me tell you the reason why it is funny...
Don't use a big word...
Don't use a big word where a diminutive one will suffice
This joke is ironic. The humor is the fact that the jokester tells the listener that they shouldn't use big ones if there is a sufficient diminutive word. This is funny, because the word diminutive is most often defined as small (a one syllable word), which is much smaller than diminutive.