be up to (one's) old tricks

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 old 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.

See also: old, trick, up