I am the same, always jeans and tee-shirt sitting in row 3, much more comfortable.
Like I said, the issue here was more that the kid was jumping up and down like a yo-yo....
I don't care about suit or jeans, but another thing annoyed me last week on BNE-MEL: I was in 3F, another WP in 3D, and luckily 3E remained empty. On the other side of the aisle, same scenario: 3A and 3C occupied, 3B vacant.
Gentleman walks in as one of the last to board, spots empty 3B (lucky he didn't have is eye on 3E), and asks FA if he could sit there instead of [whatever his assigned seat was, he was in row 6 or further back]. No idea if he was WP or SG or something. Anyway, FA tells him to take his assigned seat for take-off but she would check with the cabin manager if he could relocate. I saw FA have the chat with the manager, don't know what the verdict was but it included a lot of head-shaking by the manager. FA then went to talk to the gentleman.
Fast-forward 15 mins: Up in the air, seat-belt signs go out, and voila, 30 seconds later, Mr. X politely asks lady in 3C to please let him through and take "his" seat in 3B. Lady in 3C was definitely looking at him a bit annoyed but didn't say anything nor consult crew, just let him proceed. Not sure what 3A's reaction was.
What would you make of such a situation? Had he tried to sit in 3E I would have used the call button. WP perks are scare and rare on VA so I value this bit of extra space, it's occurring rare enough in row 3. I know there is no such thing as a WP shadow or that I don't have any "rights" over the empty seat next to me, but such behaviour supported by the crew is simply annoying and not correct.