You insult or diss someone and at the same time you big them up. Usally complimenting someone followed by a negative remark. Or bigging someone up and dissing them in the same breathe, leaving them with mixed emotions.
Craig: Yeah Shawns pretty awesome with computers, besides the fact he's a fat.
Dan: Yeah i agree. Casey looked handsome last night at the dance, to bad he smells of shit.
Bystander: You guys are good at diss ups... To bad you're both shit at counter-strike