A clag bag is the scrotum which contains the CLAG NUTS. These nuts contain the clag. CLAG is a gooey spoof like substance, mainly used whilst at school to glue pictures or cuttings into a scrap book. Through the adolescent years of learning to toss off, one notes the similarity of the jism to the viscosity of clag glue. Thus, the term for the common ball bag is morphed into the term CLAG BAG.
Jenny told me.... 'Jack Off is a real sly cunt. He grabbed my tit, so I kicked him fair in the fucking CLAG BAG/S (scrotum)'