The other day I was in line with my twin 3/yo boys and another boy, who was probably 4 or 5, leaped forward and roared in one of their faces. On the way out, they also said he touched their hair. (I had my back turned most of the time)
I didn't catch the hair part, but I did see the roar out of the corner of my eye. At the time all I managed to do was give the parents a brief "WTF?" look. They didn't seem to care. (Which is maybe why their child is a little monster.) The boys and I talked about how that wasn't very nice on the walk back to the car.
Days later, I'm still a bit bothered. Maybe not so much by the child, but by not knowing how to respond. I'm sure some parents would get aggressive and confrontational, but that's not my temperament. Plus the other party could just double-down, and it'd get ugly from there.
Perhaps a firm "Excuse me, I know you're probably just having fun, but it's not very nice to be mean to little kids."? Regardless of the result, I'm hoping it'd show my boys it's important to at least try to speak up.
Open to wiser ways to handle a situation with "bullies" / inconsiderate people.