A-Cup Angst: She appears to be rather flat-chested compared to many other nations on this page, and many fanworks have her being self-conscious about her lack of assets compared to other female nations'.
Boobs of Steel: Subverted. Romana has been said to be a better fighter than her male counterpart, but a group sketch shows she certainly doesn't have big breasts. Fanon on the other hand loves to play this trope straight.
Yandere: Pixiv fanart picked up on this a bit even before the first day he was revealed finished. One can also assume he's yandere for fem!Russia, but YMMV. The type of yandere tends to differ, though: contrasting with the canon Belarus being "let's get married, let's get married, let's get married, LET'S GET MARRIED" (obsessive type), male!Belarus tends to be more passive-aggressive and say "I'm the only one good enough for you, Sister, so let's get marriedmarriedmarried" instead (possessive type).