We're so conditioned to the phrase "That's deep" that it almost serves as an automatic response to any insightful or slightly poetic comment that could be given. Myself, I don't even like to think about thoughts, so if I hear so much as one three-syllable word form on your lips, I begin forming "That's deep" on mine right away. Now that I've saved you the trouble of stimulating a conversation, we can return to talking about drinking, video games, rock music, or other friends who aren't in the room.
And now I hear you using other complicated words, you pretentious cock. You think that girl over there, that cute one, is svelte? You call her a sylph? Fuck you. Don't you ever make my language pretty. We have words for girls like that: cute, hot, sexy. Those are them; use them.
I noticed you talking about the environment again. That isn't rock music and it doesn't affect the amount of drunk I am. You say that in 2018, solar power could be more economically efficient than coal and gas? Sounds like hipster bullshit to me. Take your highbrow smart car and your ugly Toms back to Greenwich Village or wherever it is that you weirdos come from.
...In our culture we really like to intellectually suppress each other. Maybe it's because of a natural competitiveness, in that we all wish to believe we're on a tier above everyone else. Or hey, maybe it's because we're actually on some apathetic tier below everyone else and don't care enough to approach interesting issues. But either way, I think "That's deep" usually amounts to one of the most condescending phrases you can offer another human being.