Compound noun or adjective made from waste and gash, as referring to a female vagina. Originally referring to a woman that was frigid or sexually uncooperative, quite literally,a waste of her having a gash, as noone could fuck her. This then developed to become a word used to mean all things that were a waste of time or effort, or simply sub-standard in nature. Also a derogatory term of insult, often following an action of apalling quality.
That girl was wastegash, she wouldn't even grind with me!
Man you are wastegash, you couldn't have sex wit a horny dead body.
This place is such a wastegash.
That shot was wastegash, you completely missed the goal.