Turmoil grows with muzzled mouth

I can't off the top of my head think of any scripture to help you. I think the first step you need to take is make sure you are living a Godly life. Living a Godly life fills us with confidence. Once you have your confidence, I see several options for you. If you want to say something, say it. If they don't let you speak, get up and leave, maybe even find other people to hang around. Or don't hang around anybody. I live alone and don't socialize much. I am active in my church and try to walk with the Lord, and I am content.

You do not have to "muzzle", to keep the tongue silent. Let God The Holy Spirit CONTROL IT!

Psalm 15:3
He does not slander with his tongue, Nor does evil to his neighbor, Nor takes up a reproach against his friend;

Psalm 34:13
Keep your tongue from evil And your lips from speaking deceit.

Proverbs 17:4
An evildoer listens to wicked lips; A liar pays attention to a destructive tongue.

Jeremiah 9:3
“They bend their tongue like their bow;
Lies and not truth prevail in the land;
For they proceed from evil to evil, And they do not know Me,” declares the Lord.

James 3:8-9
8 But no one can "tame" the tongue; it is a restless evil and full of deadly poison.
9 With it we bless our Lord and Father, and with it we curse men, who have been made in the likeness of God;
10 from the same mouth come both blessing and cursing.

1 Peter 3:10
For, “The one who desires life, to love and see good days, Must keep his tongue from evil and his lips from speaking deceit.