Dad keeps telling my not to sell/trade gifts?

Okay, here's the deal.

A gift is a gift, an item given to one without expectations.

The thing is, he ALWAYS ruins ANY deals I have because he thinks it'll hurt the people that gave me the gift. It might, but they won't be devastated by it.

He also over exaggerates the amount of work that went into getting me this specific gift.

Here's what it is;

My biological dad, aka the one I don't live with, bought me a laptop in 2012. Ever since I've known about them, I've always wanted a gaming PC. This MIGHT be the 4th time he's ruined a deal regarding this laptop because he always does stupid **** that makes the buyer/trader change their mind.

He KNOWS that I have always wanted a gaming pc.

I'm basically trading this, and 400 dollars for a PC, but he keeps telling me not to, because my biological dad might feel hurt, although in the past, he's said it was ok.

I'm really getting pissed off, he ruins almost any shot I have at getting what I have wanted for years.

Sorry that this was written so poorly, I just needed to type it up quickly.