"If a lion could talk, we could not understand him."
Of course this doesn't hold in Equestria, where lions can talk and ponies can understand them, for certain values of Fluttershy. But the idea behind it is useful for giving this story a place to go: we all communicate in keeping with our society and our lived experience.
The roc, then, is not trying to teach respect to a bunch of disrespectful ponies. The roc is trying to teach respect to a bunch of disrespectful weird-looking roc chicks. So how do you go about deciding what that looks like?
1) Work out how a respectful roc do.
I'm assuming you're asking because there really isn't much information on the ecology of the Equestrian roc, and you need to make something up that still makes for a good game session. Well, you're not writing Roc Emily Post here, you're trying to come up with a few simple guideposts, enough to get through in a game session and have some stuff left over. Ideally, some should roughly line up with how a respectful pony should act, and some should be more recognizably roc-specific, because the source material never wrote animals or magical creatures as completely alien, at least not when they were supposed to be longtime denizens of the world. You might consider these, in ascending order of how they might complicate your PCs' lives.
- When a roc bows to you, bow in return. Probably the easiest, unless you've got an aspiring juggler in the party.
- No mumbling. Roc mumbling, mind you. A roc speaking loudly and clearly is not quite full BRIAN BLESSED for a pony throat, but it's getting there. Might run afoul of a Quirk, might not.
- No interrupting. Pretty much the same, Quirk dangers only. Though if you wanted to switch this one up, maybe have rocs operate under standards that means ponies accidentally interrupt them sometimes - rocs often pause for a while when thinking, say, and until they've lowered their wings or said something specific they're not really done talking.
- Ask before you take something or go somewhere. This is the one that restricts their freedom the most, giving them an obstacle to overcome by trying to understand where the roc's coming from.
- No keeping secrets. An advanced challenge mode that you may or may not want to include. It means that if your PCs are trying to coordinate among themselves covertly in ways that the roc notices, the roc will disapprove.
All of these arise from a central concept of what I imagine roc society to be - that most of the time, it happens at a distance. Rocs are wide-ranging and can often be solitary, so their greetings and their conversation are long-distance and regimented or formalized to minimize confusion. At the same time, every roc has a very different personal experience from every other roc. When you're in another roc's territory, you should always be open with them about what you have and what you're doing, because what they know could save your life but they're not about to tag along with you all the time in order to do it.
If you want to come up with a different idea of what good manners means to a roc society, feel free, but it should be similarly grounded in a sketch of how that society operates. This is because you need to:
2) Be honest with your players.
Yes, if they mess things up badly enough that it gets to the "treated like recalcitrant chicks" stage you should be clear about what's expected of them - not the exact steps to take, which they'll have to work out on their own initiative, but certainly why they have to take them. I mean, you can let a little drama happen when they're snatched up and gently-but-firmly placed in some shredded-up bedding material, but after that you should lean over the fourth wall and tell them why, letting the drama into a problem they have to address. The roc doesn't intend for it to be a secret why they're being treated that way, after all - that would be terrible manners.
But aside from all that, roc society is a knowable thing, and some of your PCs might already be hip to the jive (or hit a Mind roll to get that way). Or they might possess the Charm and social grace to correct themselves based on how they're reading their conversation partner, even if they don't know exactly what the right thing is in advance (in which case, tell them why their Charm works when it's working).
In other words, don't just leave it as a guessing game about what secret acts behind your screen count as respect. If they're doing the right thing, let it count without rolling. If they're making an effort, let their character sheets try to fill in the blank. But the dice aren't always kind, for all that, so if it does reach the "recalcitrant chick" stage:
3) Teach by example and correction
If Junior's still with them, this gets easier. He already knows how a respectful roc do, or else he'd still be warming the nest. If not, there's nothing to say there can't be other chicks, though not necessarily respectful rocs yet. (And honestly? If Junior's still with them, he's probably willing to screw up on purpose, so Mama can shame him for being a bad example and your PCs can learn what a good example is by contrast.)
But ultimately this isn't a blind guessing game any more than their first impressions of the roc were. You've already told them there's something wrong with the way they're talking and acting around the roc, and that the roc's trying to show them the right way to do things.
I've already talked about how Mind and Charm rolls can help with understanding. The last relevant part of the character sheet is the Stamina count - not that the roc is going to lash out with frustration, but more of another price your PCs can pay in order to succeed. You know, through trial, error, and the sorts of love taps and wing buffets that wouldn't really bother a normal roc chick, but which over time could certainly discombobulate a weird-looking roc chick (you know, a pony), especially if the dice aren't going to let them be a quick study.