The act of pressing ones lips against a transparent surface, typically a glass window, to form a seal and then breathing out to expand the cheeks.
Generally the intention is to disgust or taunt anyone that may be on the other side of the window. Although slightly less offensive, the action is performed in much the same manner as to chuck a browneye.
"Quick, Sally's in her car, do a blowfish on her window!"
A largely benign condition whose main symptom is the appearance of deep red creases across one or more fingers, forming a continuous valley. The condition is mildly uncomfortable but generally leaves no trace beyond ten minutes or so.
Causes include carrying heavy plastic shopping bags.
Oh damn, check out this bagatitis I picked up from Woolies today.
That's some nasty bagatitis you've got there!