1) As with fuckwit, someone who is truly clueless, hopeless and useless.
2) A variant of dickhead, someone who is not very bright, but thinks themselves a great deal cleverer than they are.
3) Someone who thinks with their dick, can't control themselves and will quite literally shag any female, even the most repulvie munter.
2) What a dickwit, he thinks that an assassin is something to do with homosexuals!
3) Did you see the munter that dickwit banged last night?