Itchy mouth has a similar meaning like big mouth. It means someone can't stop gossiping or likes to kick up a fuss. It's very common among high school students and 1st year university students.
"Hey pork pie, you need to see a doctor for your itchy mouth!"
"I'm sorry teacher, I can't control myself, but you know the root cause is the school culture?
"I'm sorry teacher, I can't control myself, but you know the root cause is the school culture?
by 1st year gossip Uni. student March 21, 2009
by Mr. Terrence L. Trezvant October 13, 2003