Tattling on someone for coming in late to work is not a good thing to do and so jumping for joy about it would be considered sarcastic.
Consider the statement "I couldn't believe that my coworker told my boss that I came in to work 15 minutes late this morning. ". Based on this "I was jumping for joy when my coworker tattled to my boss that I came in 15 minutes late this morning." a true statement? Yes, no, or I don't know?