Put it at the end of a failed attempt or an awkward confession as the closing reaction, then follow it with Oh My God Wow when the moment needs a bigger escalation, or switch to Damn for a drier second beat that keeps the joke moving.
このサウンドについて
Ainnnn is a short vocal reaction lasting about two and a half seconds, centred on one stretched, sighing syllable that sounds like a weary groan. It feels exasperated and playfully resigned, the kind of noise you make when words would only make an awkward moment worse.