Slaphead can affectionately point out something stupid done by yourself or a colleague. Its that moment when you realise the problem you have spent ages trying to find is discovered and its soo simple or soo stupid and soo obvious.
Its that point whn you mentally hit yourself and say something like D'oh
I'm having a slaphead momoent: used in the context to explain to a colleague why you have just done something silly. Similar to senior moment or blonde moment, but without the justification of being elderly or blonde.
"Our nominee for slaphead of the week is........". Used in the context of a project review meeting for this weeks most idiotic error