be up to (one's) (old) tricks

To be doing things that one was known for doing in the past, especially deceitful or mischievous behavior. Food went missing from the school cafeteria? It sounds like Billy is up to his tricks again. I reunited with my two best friends after nearly five years apart, and we were up to our old tricks again in no time.

be up to your (old) ˈtricks

(informal, disapproving) be acting in your usual way, which the speaker does not like: Tom’s just been released from prison — he’ll soon be up to his old tricks again, I expect.