Why does he act serious with me when he's around me?

This other guy friend I have, lol! Acts serious around me when he's with me. He is extremely crude and jokes around a lot and I am like that too! LOL! So everytime I act crude or I joke with him he just gets silent. I tried joking around with him through texting, and he kinda jokes back, but it's not like how the way he is with other people. Like with other people he'll act crude, and show his extreme funny side, where as with me, he just shows a little bit. I don't understand that? Any ideas? Opinions? Thank you!
Why does he act serious with me when he's around me?
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