When people refer to someone else's parent as "mom/dad", especially in formal contexts.
Maybe controversial because I've never seen anyone else get annoyed by this, but it just seems overly personal and childish.
Example of what I'm talking about-- A dad goes to his child's school play. The teacher pulls him aside and says, "Dad, you can go sit over there."
Or a kid gets picked up from their book club and the instructor notifies them by saying, "Mom and dad are outside in their car."
I understand this has some functional purpose (immediately establishes that this person is the parent of someone here and distinguishes them from other people who aren't parents) but it irrationally pisses me off.
I feel like it's always better and more respectful just to ask for a name or refer to them as eg "Amy's mom" or "Lilian's dad". Even if you mess up the name or something, you get your intent across the same and avoid broaching any boundaries.
I get it if it's around a really young kid who only recognizes their parents as "mom and dad" and truly believes that's what they're named, but 90% of the time I see this sort of thing said to parents of middle/high schoolers. Those kids are old enough to know that their parents aren't literally called "mom and dad" and it makes more sense to say, "I was talking to your mom and dad today." than "I was talking to mom and dad today."