be an angel

1. To be sweet and perfect, incapable of doing wrong. No one will believe it was you who stole the school mascot. Everyone thinks you're an angel! Mom and baby are doing great. He's a little angel! I was a very rebellious teenager, so I'm quite relieved that my son is an angel in comparison!

2. To be very helpful or considerate, especially in a time of need. She saved me when I was being mugged. She's an absolute angel! You brought me coffee? Ah, you're an angel. My assistant is truly an angel—I don't know what I would do without her! She is the only reason I'm ever on time for anything.

you're an angel

You are sweet and or/perfect. You can do no wrong. You brought me coffee? Ah, you're an angel. Right, like you stole the mascot. You're an angel, and you were at the library when it happened!