Sure, it's easy. You just need to define "asking for gm", cause the computer sure as hell can't do it for you.

"can i have gm?"

"give me gm powers"

"can i be admin?"

"you need gms?"

"I would deeply appreciate it if you would empower me with the rights, rank, and priveliges customarily reserved for administrative personnel."

As long as you think up every possible combination of words that amount to someone asking for GM, the code would be foolproof.

You could make code that counts every time someone uses the letters "gm" next to each other, but that would miss people who say "admin" and boot people who are just talking about gms.

You could make a pattern recognition program and "teach" it what it looks like when people ask about GM powers... but if you're going to go through that much trouble... you're better off just booting people yourself.