How to Be a Smartass

One of the most important things to being a smartass is to keep a straight face at all times.

Don't let the other person know when you're being a smartass or when you're being serious. The key is that they won't be able to tell if you are being truthful or sarcastic until shortly after the joke.

Here are some examples.

Smartass: "Hey, I really like your shirt. My grandma has one just like it."
Oblivious Guy: "Really? Thanks!"
Smartass: "No problem! I wonder if they make them for men."

Idiot: "Wow, this hot chocolate is hot."
Smartass: "You think so? Hey, maybe that's why it's called hot chocolate."

Smartass: "Dang, have you been working out?"
Buff Guy: "Yeah, I've been doing a few sit-ups."
Smartass: "Wow, your abs are really defined. What is that like a 24 pack or something?"

Being a smartass takes practice.
Saying the opposite of what you really think is one way to go, while extreme exaggeration is another great option.

Good luck!