Is this grammatically correct? What does it mean? Any possible rephrasing? I hated this “kk” with everything in me😂 I block anyone that sends it to me… but now guess what? I use it to tease my siblings, both online and offline😂

Yes, the sentence is grammatically correct. It expresses the speaker's strong dislike for the abbreviation "kk," which they initially blocked people for using. However, they've since changed their attitude and now use "kk" playfully to tease their siblings, both in person and online. Possible rephrasing could be: "I used to hate the abbreviation 'kk' with a passion. I would block anyone who sent it to me. But now, guess what? I use it to jokingly tease my siblings, whether online or in real life!"