Lavender should have known better than to expect any sort of pleasantness out of the other girl. She was sure that all her unpleasantness wasn't just at catching Lavender at her worst, so she tried her best to remain polite. "I didn't eat dinner, so I'm hardly being a glutton." It was only a partial lie.
"What are you down here for? Did you want to sit down?" She really didn't want to sit with her, but she was trying to be nice and what else could she really say? Lavender was sure Pansy would either be snide or flat out refuse.