One who speaks in inverted commas or italics, i.e. to sound unintentionally sarcastic at all times irrespective of whatever degree of sincerity might might be intended.
(Named after John Lydon a.k.a. 'Johnny Rotten').
"Sir - may I take it that you are a Lydon... for if so, I do not appreciate the jest!"
"Nay madam, I jest not... and your culinary skill is only surpassed by your unfading beauty."
"Ye git - now I know you're taking the piss!"
From "The Importance Of Being Sarcastic" By Oscar Wired.