About my flight neighbour?

[ReasonablyIntelligent]

Just boarded an 8 hour, overnight flight.
I'm flying solo and on the aisle seat.

I get to my row and find a strange man in my seat, the seat next to him (middle seat) is empty.
He initially tries (quite aggressively) to deny that the aisle seat is mine, but eventually relents and moves over to his spot.
He takes both blankets and both pillows with him.

I get seated and then ask if he could kindly pass my pillow and blanket (both stashed about his person). He denies having either and demands that I check my seat because I'm "clearly not looking properly".
Whilst I perform a polite seat sweep (God knows why, I can see the fucking pillow) he slides my pillow behind his back and then drops the blanket to the floor and kicks it under his seat .

Having no idea why I've offended Strange Man, I decide to juts play dumb and ask an air steward for a new set. No bother, though they're super busy so I'll imagine they'll forget for better things to do.

Strange Man has now proceeded to man spread in such a way that my shoulder is at an odd angle from my seat and my legs are skew whiff.

I am not a ballsy person. In fact, I have a fairly strong social anxiety.

There are no other seats on the plane.

AIBU to silently seeth, or am I being a right wet blanket?

On a short haul flight I had the man in front throw back his seat as soon as we were airborne. I have joint issues so after an hour started to struggle. I swapped with DH.
Man in front went to the toilet and on his return swapped with his wife, so was again in front of me and reclined himself again. I politely asked that he didn't as I was now in pain and was told that he was 'comfy'.

Ladies and Gentlemen, I give you my Brother In Law. One of the many reasons I have nothing to do with any of them anymore.

Well done OP.

The airline would do nothing!
He’s a frequent flyer....it’s likely your complaint would get ‘lost’

You handled yourself really well, was so glad to see your update.