The polite way of telling someone they're a
dumb ass without letting them know you're
thinking they have recently acted or spoke without using even an nth of thought/brain
activity.
Act:
Your best friend insistently waving at your mom as you drive past her in the Walmart
parking lot while
skipping school.
BFF: Look! It's your mom. (Waving and yelling, "Hey Mrs. Connor")
You: Yeah but we are supposed to be in gym class right now, Silly!