a syndrome most males have where they tend to act as though they're thinking with their dick (it has a head as well) instead of their brain. This usually results in them pretending to be a nice guy just to get laid, lying, etc.
Dick head syndrome is when You meet a guy and he tells you he doesn't like having sex unless it's really meaningful so you wait a couple weeks and after you've slept together he doesn't talk to you anymore. He has dick head syndrome.
He actually is married, but he told you he is single? He must have Dick Head Syndrome.