I hate it when people say 'Join the Ma j' or 'I'm in the Ma j' because your not, your in the Ma. Ma stands for Mob Arena, J stands for Join, so all your saying is 'Join the Mob Arena Join' or 'I'm in the Mob Arena Join'
My teacher used to say "Lets go in the PAC center for practice" and we'd all cringe because PAC is Performing Arts Center, and yeah it was bothersome xD
Doesn't really matter at all. If you say "Join ma" or "Join /ma" its not the right command and people might not understand what it is. Saying /ma j tells the command. It may be cringy to see "Join /ma j" but it is helpful.