The story
Derisively mimics the frequent perfect conditional forms (I would have done this and that) which are used when discussing events that may have occurred in the past.
Etymology from Wiktionary, CC BY-SA 4.0.
woulda, coulda, shoulda
Today it means: An expression of dismissiveness or disappointment concerning a statement, question, explanation, course of action, or occurrence involving hypothetical possibilities, uncertain facts, or missed opportunities. Full definition →