shoulder biter
'Shoulder Biter' (Shoulder biting) 
An action usually undertaken by a wheelchair bound retard. Because they cant keep their necks straight or mouths closed, they usually wheel about literally biting their own shoulder(s) .. 
Heather: 'Jesus Steve, that freak in the chair over there really is a shoulder biter

Steve: 'I know, reminds me of that freak at work, Janet'