In "Chapter 16" of The Mandalorian, Boba Fett taunts Bo-Katan Kryze by repeatedly calling her "princess." Given that this is the first time they've met in-universe in The Mandalorian, the question of why Boba Fett defaults to this insult in particular is a particularly interesting one.
When Fett and Kryze encounter each other in "Chapter 16," tensions are immediately high. The moment that Boba Fett speaks, Bo-Katan calls him out by saying, "You are not a Mandalorian." Fett's voice immediately tips Kryze off that he's a clone of Jango Fett; since she fought in the Clone Wars, there's no doubt that she'd instantly recognize what they sound like. When Kryze calls Fett's father his "donor," Fett warns her that she's crossing a line by saying, "Careful, princess." Was this a simple way of Fett topping Kryze's last insult, or was it a direct reference to Bo-Katan's history with the Clone Wars?
In The Clone Wars animated series, Bo-Katan's sister, Satine, ruled as the Duchess of Mandalore. Eventually, her sister was overthrown and imprisoned by a branch of the Death Watch, which was also subsequently overthrown by Darth Maul. Once the Republic drove Maul out of Mandalore, Bo-Katan finally became the Regent of Mandalore. However, she lost this title when she refused to fall under the rule of Emperor Palpatine. Eventually, Bo-Katan came into possession of the Darksaber, thereby becoming the Mand'alor and sole leader of the Mandalorian people. After the Great Purge, Bo-Katan lost possession of the Darksaber, thus losing her title and claim to leadership.
Though Boba Fett was young during the Clone Wars, he was still somewhat present in the action. After failing to assassinate Mace Windu to avenge his father's death, Fett was imprisoned on Coruscant for some time. While he would've been pretty isolated from the main events of Clone Wars in prison, it's not impossible that rumors of Bo-Katan and what was happening on Mandalore might've traveled far enough for him to hear about her. There's also the possibility that Jango Fett, who was a real Mandalorian, could have told Boba stories about the planet and the New Mandalorians, who were led by Satine Kryze. If that's the case, then Boba calling Bo-Katan "princess" is actually a very pointed slight at her personal history with ruling Mandalorians.
Alternatively, Boba Fett might've just caught on when Din Djarin tells Bo-Katan that helping them rescue his adoptive son Grogu might "be helpful in [her] effort to regain Mandalore." The tone of the room noticeably changes as soon as Djarin says this, and Bo-Katan, Koska, and Boba soon break into an all-out brawl. Clearly, ruling Mandalore is a touchy subject for all fighters decked out in Mandalorian armor involved. Currently, it's still unclear if Boba's jab at Bo-Katan's past was intentional, but one thing is pretty likely: there will certainly be a whole lot more of Bo-Katan's journey next year in The Mandalorian. And who knows if she might cross paths with Boba Fett again in The Book of Boba?