That's really interesting, because to my ears it's the opposite. Where I grew up (Frankfurt area) 'was guckst Du?' was a stereotypical prelude for physical violence (going along well with 'auf's Maul, oder was?'). 'Blöd' to me sounds way too weak for that type of scenario. But context and tone matter a lot in either case.
Also, i think there is a geographical difference regarding the usage of verbs for looking. 'Schauen' is standard in the south, but sounds quite formal to northern ears (at least for spoken language). At the same time 'gucken' is standard in the north, but may sound diminutive to southern ears (I guess?).
To convey the aggression of someone yelling 'what the fuck are you looking at?', I would probably go for something like 'was guckst Du, Arschloch?'