People forget that Terezi was nice to Tavros, tried to boost his confidence a little and was genuinely enraged when Vriska maimed him (and killed Aradia). She thinks he's lame but she makes an effort to not let it show and makes a good faith attempt to resurrect him with a kiss even if she thinks it's gross. She's nice to Nepeta as well, humors her roleplaying and can't bring herself to let on that she's being facetious.
Terezi is nice! She only dishes it to people she thinks can take it and give as good as they get: Karkat, John, Dave etc. She doesn't punch down. It's like a whole aspect of her character that gets lost in fanon.