know what (one) likes
To be very certain of or rigid in one's tastes or preferences, even if it goes against conventional wisdom. A: "You know that white wine goes much better with fish, right?" B: "I know what I like, and I like red wine, so that's what I'm getting!" My daughter insists on wearing a fedora to school. The kid knows what she likes!
know what you like
have fixed or definite tastes, without necessarily having the knowledge or informed opinion to support them. 2002 Sunday Herald We adjourn to Starbucks where…I know what I like (grand skinny latte, £2.15).