The mouth is very quick to heal, but I would think it would totally be possible to destroy a few taste buds by burning them repeatedly. Also, different parts of the tongue sense different tastes so maybe it's possible that you have damaged some parts but not others? I ain't no doctor, it's just a guess. Here's a spiffy illustration:
It is also possible that some of your friends are
Super Tasters, while you are not. Super tasters "experiences taste with far greater intensity than average." These people, myself included, usually find things like broccoli, grapefruit, coffee, some alcohol, etc. to be bitter. I HATE grapefruit because it's so much worse than eating a sour patch kid, and can't drink coffee without ample amounts of sugar and creamer because it is too bitter. I can taste and smell some things that other people can't, just because one of my parents happened to also be a super taster. Crazy genetics!
Get yourself a strip of paper laced with phenylthiocarbamide (PTC) and stick it on your tongue. If you sense bitterness, you're likely a super taster. If not, then you're with the majority of people.
And stop burning your damn tongue.