To "do a staggy" is to cut your arms for attention, and, specifically, to cut your arms only to then roll up your sleeves and show it off. Thus, to demean those who hurt themselves and are then ashamed of it, to a point where they don't shove it in people's faces.
A staggy can also refer to an attention seeker in general, or a general pain in the backside.
"I fell down a hill and hurt my hand, and it really looks like I've done a staggy. Shit."