pip-squeak/ pipsqueak (noun) – small or unimportant
(a pip is the seed of an apple or other fruit, and squeak is the sound that mice make. I don’t know where the word pipsqueak comes from, but it sounds funny, doesn’t it?)
Here are some examples of how you can use it:
Do you really think I’m afraid of your pipsqueak brother?
Pluto being such a pip-squeak of a planet, scientists at first didn’t want to call it a planet at all, but proposed the name dwarf-planet.
On the screen the actor looks so tall and attractive, but when I met him I was disappointed he was a little pip-squeak.
Aw, look at that little pipsqueak puppy. He must be only one week old!