All of Bruce's kids have come out to him as some form of homosexual that when it comes to Duke, Bruce just assumes he's queer and is too scared to tell him for some reason.
Sure, literally everyone in this family, including Bruce, are publically out it's still normal to be afraid to come out and Bruce thinks he just needs an extra push.
He starts asking Duke things about his love life, starts saying shit like "I'm always here for you, you know that right?" and even resorts to dumbass shit like leaving little rainbow flags in places he knows Duke will find them.
Duke: guys, Bruce is acting really strange.
Jason: he's always acting strange. It's Bruce.
Duke: yeah but like extra strange
Duke: idk man he's like, being strangely supportive. Like in a creepy way. And he keeps asking if I have a "lover" and what my type is. It's really weirdly invasive and I don't know what to do
Jason, starts laughing hysterically:
Steph, wheezing: holy shit
Dick: Duke he thinks your gay and he's trying to see if you'll come out to him
Duke: but I'm not gay ????
Jason, still laughing: I think he just assumes any kid around him is some form of gay at this point
Damian: I suppose none of us are heterosexuals
So, Duke has to sit Bruce down and break the news that he is straight and exclusively likes girls. Bruce is surprised, thanks him for telling him and now says shit like "I know it's hard but we can get through this"
Jason, who is still laughing: you had to come out to Bruce as STRAIGHT. This is the best day ever!