Be somebody’s strong suit
Definition 1 of 1
Pro Tip 1/3Figurative Usage
The phrase 'be somebody’s strong suit' is often used figuratively, not literally referring to clothing or card games. 
Cooking isn't John's strong suit, but he's great at barbecuing.
Pro Tip 2/3Negative Form
Using 'not my strong suit' is a humble way to admit a weakness without seeming overly negative. 
Negotiating is not my strong suit, so I need some advice.
Pro Tip 3/3Subjectivity
What is 'someone’s strong suit' can be subjective, varying based on personal opinion or social context. 
In her opinion, creativity is not his strong suit.