Normally signalled by a large release of breath follwed by the exclamation "Booooiiillllleeeedd" in a high pitched tone.
A boiled head can be cured by beer, sleep or a "reflection hour" where the topics that have boiled your head are discussed with friends
See also cooked ,stressed.
Dude 2: Isn't he working duty til 10pm?
Dude 1: Oh man he must be BOILED!
*Mike walks in*