Sirius let their words roll off of his back. The point was that he was getting to Snape, and that pleased him. What didn't please him was the thought that a Gryffindor would ever be friends with a Slytherin. It was... it was... it was downright unnatural! Yes, that's what it was. An abomination.
"Can James help it he's popular?" He plopped himself back onto the ground, this time assuming a lotus position. Good thing he didn't carry any books on a regular basis, they'd just be in the way.
He pulled out his wand, and drew a heart in the air, a pretty sparkly thing. Inside the heart, he wrote JP + LE. And then he added an arrow for good measure. It hung in the hair rather nicely, and he was proud of himself for having got it right. He did practice his spells, just not necessarily the ones he was meant to be practicing.
He didn't bother arguing with Lily. He'd learned that trying to be logical with a female never came to any good - they just weren't. Instead, he smiled enigmatically, and said, affecting a slight lisp for effect, "Methinks thou dost protest too much, milady." Snape, he simply ignored.