"cons" is not just not a "reddit acronym", but is also a common term for "conventions" and "conferences" that has been in use for at least three decades. I haven't lived longer than two and a half but I wager it's older than I am.
You're not entitled to your own ignorance, and not everyone uses language the same way you do. Please lighten up, open your mind a little bit to that, and grow a thicker skin.