Polite vs. Casual

Every time I talk to a native Japanese person (outside the classroom), it becomes harder and harder to keep speaking politely. My teacher wants me to learn only polite language for now, and I totally understand and respect why. I know that polite language is, by nature, never going to be rude, so it works in every situation. Also, I come into contact with Japanese people at work, and I need to be polite to them because they're customers.

THAT SAID,

I feel so impersonal and removed and stuffy when I'm talking to my friends. I think they understand why, but it still feels like it's a barrier between us. I mean, can you imagine this conversation in English?

A: Hey, girl, wassap?

B: I am having a nice day.

A: That's cool. So what've you been up to?

B: I went to school and enjoyed that. However, today I am tired. We are having nice weather today. And you?

A: Oh man, this asshole came up to me earlier and was all, "Get off the sidewalk!" and I was like, "Man, some people."

B: I am sorry to hear that. That is very strange.

I mean, seriously. From trying to speak Japanese, I know exactly what B's intended words and meanings were, but they just come out so dry and completely devoid of personality. I mean, reading that conversation, would you think they were close? It's hard to tell because their language is entirely different. B sounds like some foreign adult, honestly.

Anyway, is anyone else having this issue?

My survival plan is to be exposed to casual lingo (like, I'll have my conversation partner teach me both the polite and casual version of things), but I'll only write down or really pay attention to the polite one since that has to do with the studying I'm actually paying for help in. I figure if I keep hearing it, I'll be able to compartmentalize everything soon. For instance, I know "chou" is the casual of "totemo." And I've started picking up on verbs--they straight up just don't conjugate them most of the time, so that's easy to remember.

Let me know if you've run into this problem. Any solutions?