Marcel over at Aggie Catholics has a helpful post about applause during liturgy. While it’s frowned upon—the pope is not a fan of it—there are a few instances when it might be acceptable:
Clapping is usually done for a human achievement and is not for God. So, it is a misplaced act in most liturgies. There are some places where it is explicitly allowed though. For instance, in the Rite of Ordination for priests there is an exception for the USA where the congregation can show approval of the act of choosing the men to be ordained and one of the ways proscribed in doing so is applause.
That noted, there are a few other instances when applause is, in fact, appropriate:
The lector announces that there is no second collection.
The sound system fails during the homily.
The crying toddler in the back calms down, and his mother didn’t have to give him cookies.
The Teen Club arrives early and no one is wearing a tube top.
The priest announces that the guitarist and bongo player got stuck in traffic.
The deacon, rising from his knees, doesn’t trip over his alb.
When reading the line about “buffets and spitting,” the lector doesn’t make it sound like he’s describing a dining option.
These are just a few. Other opportunities may arise for polite, respectful clapping.
Just use prudential judgment. You’ll be applauded for it.