Exactly as the title says. I'm looking for a BL/yaoi where the seme is a tsundere but damn caring but just doesn't accept or show.
Ugh I love that kinds fluff. Yaoi is fine as long as the above criteria match.
Please any recs....

I can't really claim to be all that much of an expert on this particular setting, I read mostly stuff that preferably has as little clichés as possible (and avoid set roles) but I've gone through a huge load of stuff through the years so I've come across quite a lot. Trying to come up with titles, but just a few come to mind, though.

It also kind of depends on HOW tsundere you want the top. Like; a real douchebag or just plain old grumpy. If also taking "fluffy" into consideration, it becomes a bit trickier. (Like, there are quite a few titles I really like, but the proportions of A-hole vs. sweet guy, are so extreme that there really is close to zero cuteness.)
I love tsunderes but on the other hand, I dislike tropes, and it's kind of hard finding stuff that meets both criteria.

If you're okay with "not really all that tsundere perhaps, but the silent grumpy type that melts", check out "Here U Are" by D-Jun. Very cute. (Also has an extra little plus; D-Jun being a guy. Male BL authors are so rare.)

"BJ Alex" sure isn't the greatest story, but it does feature what you want. The top is a real piece of work... But he kind of redeems himself a little bit, at least. Smut. (Graphic.)

"Hidoku Shinaide." I like Nekota Yonezou's art and I do read her stuff, but she does annoy me a lot at times. If you can get by the very questionable start of this title, you'll find what you were looking for. Maya is very caring, but he sure wraps it in a LOT of unpleasant traits... -__- Smut. (Graphic.)

And I guess, the ultimate match for what you asked for... "Gravitation" by Murakami Maki...
Old, classic, not really a great story and contains a shiiiiiiitload of completely irrelevant and stupid plot elements, but Yuki Eiri is pretty much the epitome of tsundere. It was one of the first BLs I read back a loooooong time ago, so I kind of love it, but I really don't think it's very good...
But Yuki... oh my. He will forever be my fav tsundere character.

Ah, my brain doesn't cooperate with me right now, I'm looking around for recs myself and my head is filled with totally different types of BL. If I think of anything, I'll add it.