Anyone meanspirited is unkind, not particularly generous, or even deliberately rude. A meanspirited person might steal your place in line, or even kick you while you're down.
It's meanspirited to crush someone's good mood with a nasty remark, and it's also meanspirited to eat your huge lunch (and refuse to share it) in front of a hungry classmate who's left his at home. Acting in an inconsiderate or careless way, particularly when you show a lack of generosity, will make you appear to be meanspirited.