be (not) (one's) bag
slang To be something that one is interested in or enjoys. Usually used in the negative. Dancing just isn't my bag—I always look really foolish. You can tell just by looking at her that fashion design is her bag.
not be someone's bag
INFORMALIf something is not your bag, you are not interested in it or are not good at it. They're a very successful band — they're just not my bag. `Being an umpire is not my bag,' says Anders. `I'd rather be a player.' Note: This expression may have originated in the slang spoken by American jazz musicians. They sometimes referred to the type of jazz they played, or to their own style of jazz, as their `bag'.
(not) your ˈbag
(informal) (not) something that you are interested in or good at: Poetry isn’t really my bag.