An expression of dismissiveness or disappointment concerning a statement, question, explanation, course of action, or occurrence involving hypothetical possibilities, uncertain facts, or missed opportunities.New York Times, May 15, 1994): The order of words in this delicious morsel of dialect varies with the user. . . . In this rhyming compound, a triple elision does the hat trick: although each elision expresses something different, when taken together, the trio conveys a unified meaning. Shoulda, short for should have (and not should of, which lexies call a variant but I call a mistake), carries a sense of correctness or obligation; coulda implies a possibility, and woulda denotes conditional certainty, an oxymoron: the stated intent to have taken an action if only something had not intervened. . . . Taken together, the term means 'Spare me the useless excuses.'
(This stems from expressing that someone could have, would have and/or should have done something)
woulda, coulda, shoulda