God desires for our speach to be thankful, uplifting, and full of grace. So, instead of being sarcastic, find something to appreciate, praise, or just don't say anything. "Come and hear, all ye that fear God, and I will declare what He hath done for my soul." (Psalm 66:16)
Use your speach to testify what the Lord has done for you, to praise the Lord, and to share what you are learning from the Lord with others. In Ephesians, Paul encourages us to give thanks, rather than to speak foolishly, which is inconvenient.
Ephesians 4:29 commands that we use edifying words, to minister grace to others. The greek word for edify literally means a "structure, architecture, or confirmation". Since there is no gray area in speach, and you are either blessing or cursing, choose to edify, or build someone up with your words.
Now, if you're thinking like me, you're about ready to give up, because, like James says, the tongue is hard to control. But, God gives us a solution for this too. "Out of the abundance of the heart, the mouth speaketh." By memorizing, meditating on, loving, thriving on, God's Word, He says that you will talk wisely, and speak with knowledge.
Remember: God will not call you to do something (or not do something) that He will not give you access to His power in order to complete it victoriously.
*Note: this is just a short synopsis of the study. For more information, leave a comment.