How do you say this another way?
Why are you tripping?

Does it mean;
You can't say the words properly.

Question

How do you say this another way?
Why are you tripping?

Does it mean;
You can't say the words properly.

Answer

No.  It's slang.  Check out https://www.urbandictionary.com/define.php?term=tripping for more information.

Said in another way:  "Why are you acting so crazy? or why are you freaking out?"

If used literally, however, it would mean 'why do you keep stumbling or falling when you're walking?' but I don't believe this is the case here.

Answer

The phrase "tripping (or stumbling) over your words" means not being able to express your idea clearly. A person might "trip over his words" when nervous or tense.