This teacher? Doesn't care.
Which results in me tells the kids to throw their gum out, and then I get, "But Mrs. X lets us!!"
My usual reply? "I'm not Mrs. X am I?"
They really don't like that reply.
But gum? Hate it!! Makes people look like cows chewing on a cud. Not attractive at all.
Subbing would be easier if ALL the teachers would just follow the school rules.