A sniveller is someone who cries or sniffles a lot, especially in a way that annoys other people.
The word sniveller is not very nice. It makes people think of someone who is weak or annoying.
Examples:
The sniveller was crying loudly.
Don't be a sniveller, be strong!
The sniveller was always making a lot of noise.
The sniveller was crying so much, it was like a big rainstorm!
The sniveller cried so much, the whole room was wet!
The sniveller was always crying, like a baby.