Tatsumi is definitely the hottests and most tsun tsun [least dere dere -except a lil in recent chapters] but when it comes to not admitting feelings I'm pretty sure Onodera Ritsu is more annoying and Misaki Takahashi levels the same when it comes to shyness. Tatsumi is my favourite though, but his tsundere is on another level because he doesn't just shy away from love in general or from his seme, but he completely fools himself into thinking he could never be gay. He is somehow a queen uke, except in bed, unlike most other tsundere.
P.S. my first yaoi anime, given to me by my bi ex-bf, Junjou Romantica, followed by Sekaiichi Hatsukoi, Love Stage & then Haru wa Daite Ita, Foreign Love Affair, Sex Pistols, Viewfinder, Okane ga nai, only after that Koisuru boukun & others.
Souichi Tatsumi is the epitome of tsundure. He should be the king and rule all tsundures on Yaoi.
Koisuru Boukun is the first yaoi anime I've watched and the reason why I'm now into reading Yaoi manga because I wanted to know what happened to them, after that I started to notice and read other mangas and the rest is history. How about you?