Like that. if you push CTRL + Enter, then you will post the comment.
Also, Put a space between the ":" and dialog. And smiles will go away. Preview/Edit button helps.
Celestia: I am very disappointed in you.
Me: I know...
Luna: What is the matter sister?
Celestia: He only lasted 30 seconds in a no-blinking contest.
Me: Why is that my fault?! >:T
Luna: That is the most ridiculous reason I have ever heard for somepony to be annoyed at somepony else!
Celestia: I'm disappointed! I wanted banans! not Pie. But what flavor?
Pinkie Pie Flavor!!! DUN DUN DUUUUN!
twilight: were invaiding luna's personal space by reading her dairy.
celestia: do you even have any bananas?
twilight: im afraid not.
celestia: im very disappointed with you twilight.
She got vanilla icing instead of chocolate.