Any festy looking peenie, unwashed or smelly peenie, peenie with cheese, male STD, secretions from the peenie, pimples on or near the peenie, or even just a really embarrassingly small peenie can be said as having penisitis.
*Please note, if a wang gets penisitis, it is then classed as being a peenie, not a wang* (Please refer to PEENIE)
"Oh my God!! Have you seen Andrew's cock? He has a nasty case of penisitis!!"
"Dude, you might wanna go see a doctor about that, it looks like you got penisitis"