This phrase is used against someone, for example, if someone is trying to justify that something they are doing is the right thing or that it's okay to do it, but the facts point out that it is not the right thing or for some reason it's not okay, then this phrase may be used: ( this person is in denial) a) It's okay for me to smoke because I go to the gym every week and work out, at least I keep fit. b) Oh well, you would say that, wouldn't you? This phrase most probably originated from a famous legal case "The profumo trial" when Lord Astor denied having an affair with Mandy Rice-Davies, her response was, "well he would, wouldn't he?" Meaning - of course he's going to deny it. The phrase has changed from " he would, wouldn't he?", to "well he would, wouldn't he?", to "well, he would say that, wouldn't he?"