Somebody that masturbates in a place or situation that is very obvious, but thinks that either nobody will notice or that it will be too awkward for others to say anything. Usually found on school trips, in group hostel dormitories, in prison or anywhere else you are forced to sleep in the same room as other people.
A: Phangks u!
B: What? You want to plank me? Is plank a verb?
A: nu I mean thanks
B: Why would you use a nonsensical form of a word that is longer than the actual word itself?
A: bcs im so smart and cunning!
B: STFU.
Equivalent to the term idiot, phank can be used as a noun, a verb, an adjective, an adverb, or onomatopoeia. One can act like a phank, smell like a phank, possess the quality of being a phank, etc. It's an insult if used as a noun.