Active and competent example: Rocket Raccoon. Side character. Irascible. Not an anti-hero .. he's just from a species that isn't traditionally known to be social in the first place (perhaps his mother was kidnapped from the forest rather than a city, his MCU-specific backstory is unclear), he doesn't even know he's part of a larger species of creatures not really too much different from himself, and has been treated like a freak by the oddly shaven-apelike aliens of the MCU universe, so of course he has an abrasive personality. One might feel sorry for him more than they actually "like" him.

Doesn't have to go too far, and probably shouldn't, into the realms of comically hated or vile, but just make him or her have some attitude or personality problems

Heh my favorite sci fi book series is The Gap Cycle where two of the three main characters are completely awful people and nobody is really "good".

My one line description of the series is X-Rated Star Wars (but harder sci fi) with a lot of rape, torture, and lovingly detailed graphic violence.