Shlubs are people who are not very good at what they do, or who are not very important.
Calling someone a shlub is not very nice.
Examples:
He is such a shlub, he can't even tie his own shoes.
The boss treats us like shlubs.
The shlub always forgets his lunch.
I felt like a real shlub when I tripped over my own feet.
The shlub never gets anything right.
The shlub's shirt was on backward.