Taken from a "
dave" person who used to say hiya to all and everyone in rather a shrill voice - the term then
rolled round in that everyone would then say "hiya dave" to him mimicking his shrill voice
hiya or "hiya dave" then also came to be used to mark an act of outstanding stupidity or incompitence - followed by the sticking of the tongue in the lower lip (
like in the spacker call)
Used in the similar vein as "der" would be used