/ij

From / + abbreviation of inside joke, using the tone indicator format of slash-prefixing set by the earlier /s (“sarcasm”).

/ij

1. (Internet slang, tone indicator) Denotes that the preceding statement is an inside joke.
   • 2023 September 18, @superaquachick, Twitter‎^[1]:

     who wants to do the steal books at 3am challenge with me /ij