An expression to be used against peers when they've wronged you. Best used alongside the 'son of a' curse. Not as harsh as 'bitch' but enough to get your point across that they're being a cheeky bastard.
"whas that Dave? you eating my biscuits again... you son of a lumgumgumgum!!"
"that son of a lumgumgumgum just gave me chlamydia"