It should be: dog , pussy is the best I swear man that shit changes your mood
If you don't put the comma after dog, then it looks like you're talking about a dog's pussy. By putting the comma, the reader knows the speaker is using the word dog as a nickname for a person, and is telling "dog" (a person) about how much they love eating pussy. The comma is necessary for clarification.
Let's eat Grandma vs. Let's eat , Grandma
Help robbers! vs Help , robbers!
etc.