coulda

Short for "could have".

Meaning: would have, could have, should have
A reply you give to a whinging person who is expressing regret for not having taken a particular course of action when the opportunity originally presented itself. They've suffered the consequences and they are possibly fishing for sympathy or simply beating themselves up about it.

It essentially means, "Too late for regrets, you can't change the past, get on with your life, learn from the experience, make better choices in future, stop doing a post mortem on your life."

Meaning that it is of no use to dwell on what should have (shoulda), could have (coulda) or would have (woulda) happened/been done.
Said as an attempt to shorten a discussion that focusses on the past, thus providing no solution to an actual problem.

having an opportunity and not taking it, thus regretting it later; usually used when someone is saying to the person who missed the opportunity.

Dismissing a something you could've done, instead of dwelling on it

stupid line from the V8 vegetable juice commercial or what a V8 guy says to a tuner kid or some dick who gets a V6 in a Ford Mustang, Dodge Charger or a Chrysler 300C

An expression used in situations where one could have avoided a poor, destructive, or unpleasant decision by smoking hash oil instead. Kind of like the V8 commercials, except replace V8 with oil.