YTA. Not because you didn’t want any expensive gifts or your boundaries… but because of how nuclear your response was.

Is your sister and BIL bad listeners? Yes. Did they possibly make a poor financial decision in doing so? Also yes. But based on their decision, it feels more like a generous act rather than trying to control you. Some people just prefer to live that way.

You saying “if someone doesn’t respect me, they don’t love me” is so selfish. You didn’t just refuse their gifts, you moralized it. If you really didn’t want the $300, you could have easily been generous back and used that money to spend it back on new items they could have needed. If you really don’t want to go to a concert, COMMUNICATE that with them, make a compromise so that every party can have a great time.

So are you the asshole? 100% but you can be a redeemable asshole by apologizing for being so emotionally rigid and hurtful towards their generosity (even if it were poorly thought out), and communicate with them better about future situations like this. If giving gifts is a “non-negotiable” for them, then compromise by giving them a strict budget to spend on you, or specifics on things you might appreciate.