TikTok's feed moves fast, and a caption gets read in under a second before someone scrolls past. A line of flipped text breaks the visual pattern of every other caption on the screen, which is the entire reason it works as a hook — not because it says anything different, but because it looks different for the half-second it takes to register.
In a caption, flipped text works best as a short punchline under a straight setup — the contrast between normal and flipped is what catches the eye, so flipping the whole caption removes that contrast and just makes it harder to read. In a comment, it works differently: a flipped comment on someone else's video tends to get noticed and pinned precisely because it looks unusual against a wall of normal replies, so a short, punchy one-liner outperforms a long one.
Hashtags lose their function when flipped — a flipped hashtag is no longer machine-readable as that hashtag, so it won't file your video under that tag's discovery page. Keep hashtags normal and flip only the sentence around them. The same applies to @mentions: flip the joke, not the username.
Normal setup line, then a flipped punchline, then your normal hashtags below — that three-part structure keeps the flip functional as a joke rather than an obstacle. Type your punchline into the generator, copy it, and drop it straight into the caption field.