Obviously, you did nothing wrong and that couple are certainly well beyond the clueless-and-merely rude American traveler.

An observation: Since America generally made it impossible to institutionalize our mentally ill population, it can be dangerous to even mildly answer or reply to (or heaven forbid, escalate) bad behaviour. Not saying you did, and if you WERE going to further annoy a crazy person, do it at the airport or at arrival when there is lots of police nearby and no in-flight danger.

Personnally, I travel light and use carry-on only, and when I want to grossly abuse an airline's carry-on limits, I make sure it's an foreign carrier, overseas, and I have a ticket in biz class were FA's are more willing to indulge me. (I have been known to drag a large bag and check-in size roll case up a 747 staircase to the upper deck.)