Not much a flight attendant is going to do when they paid for their seats just like you did. They can talk all they want.
Although they were being rude.
I was on a flight back from Amsterdam years ago and these two fat old ladies were behind me and my then girlfriend. They tried to force us to keep our seats upright, as they were too fat, they called the flight attendant to complain. So I told them sorry I'm 6'6" and this seat is broken anyway, so no go, but the girl I was dating at the time complied.
These two fat twats ended up kicking her seat over and over to the point where I finally turned around and looked right through the gap in the seats and glared at them. They stopped for a little bit..then I went to the bathroom and I see this bitch literally kick the fuck out of the seat where my gf was, there was definitely no reason for it, so I took a couple steps back towards her seat and kick the fuck out of it. Then went pee and came back.
She uttered some bullshit about my then gf being a spoiled little bitch. And threatened to call the flight attendants on us because we had our seats back on a 8-9 hour flight. So I turned around and had words with both of them right there. Got the attention of everyone on the plane. Told them we would do whatever the fuck we want in our seats that we paid for and if they were too fat or inept to do anything about their situation it wasn't my fucking problem. Then I told them to call the flight attendants over. And they shut the fuck up. And about 90% of the people around us were cheering.
I know I went off on a tangent, sorry about that.
You did complete your petty revenge, but keep in mind, they paid for their tickets just like you. And they are entitled to do whatever the fuck they want in those seats as long as it's legal.
So +1 for petty revenge, just keep in mind that you're acting a bit entitled.