I wouldn't go buy a new microwave just to spite the brand. For one, Frigidaire isn't significantly less reliable than the other major appliance brands - they have noticeably worse "fit and finish" in their build quality (I don't think I've ever seen a Frigidaire Pro badge that was on straight, ever. Their french door freezer doors will not line up with even perfectly adjusted fridge section doors. etc.) but also typically a lower price point. Just about all appliance companies make some shit-boxes - from stats I've tracked at work, the common consumer brands in the US have roughly 10% failure rate for the first year, and about 30% failure rate over 5 years. Those rates stay pretty consistent between brands (as soon as someone looks like they are going to upset the balance, they release a fancy new design for an ice maker or something that just shits all over the bed and has to be 'service-bulletin'ed to consumer reports hell and the stats wander back into line).
Basically, if the thing is working now, I'd keep it until either it doesn't work or you just really want/need some feature it doesn't have. Buying a new appliance is just going to be giving money to a different-but-still-shitty brand.
I've pondered that question a LOT... Did he think it would somehow make me go out of my way to spend time with him out of some sort of primal urge to compete with my brother? Is he a psychopath? Is his brain so fucked he thought it was real?
Sad part is, I bet he doesn't even recall doing it, and he was just bored at the time.