shiny

Killjoy slang term, basically a synonym for cool

"Hey, I managed to snag a super shiny pack of multicolored eyeliner yesterday- wanna try some?"

milkshake

Killjoy slang term; basically just means "awesome"

"Dude, did you hear that band is releasing a new album?"
"Yeah, their music is super milkshake. They're not as good as MCR, though."
"*deep sigh*"

Killjoy

speaking from experience here: a feral dumbass. with good music taste tho. probably a scene kid and/or emo

"Hey, you know that kid in math class? Xe said something was 'fuckin milkshake' and I have no clue what xe meant."
"Oh, yeah, xe's a killjoy. Xe just thinks it's awesome."