Sorry about the delay in answering this one, but, let's face it, it will be a long time before the letters come up again.
I don't think
slaphead is used much in Australia - I wasn't aware of it. But it's certainly found in a number of dictionaries as a disparaging term for a bald man. The other meaning is alluded to in Wiktionary:
(UK, slang) A euphemism for getting caught doing something stupid; any individual who annoys and frustrates others to the point of making them want to slap their own heads
I don't rely too much on Wiktionary as an authority, since anyone can contribute to it and (unlike in the Wikipedia) there seems to be no expectation that sources or references will be supplied. However, the other meaning is well-supported, so
slaphead will be added to our list.
