What does Hermione do?

She creates a distraction.

Romilda Vane sat across the table, smirking at Hermione. The candlelight gleamed off her dark curly hair. She knows perfectly well I've lost my skirt, Hermione thought, and instead of helping out a fellow Gryffindor in need she's just sitting there laughing at me. Well, let's see how she likes it.

She nudged the packet of nuts with her elbow, sending it tumbling across the table towards Romilda, who had turned aside to giggle with her friends Lavender Brown and Parvati Patil. The packet slid onto Romilda's lap and she looked up, startled. Exactly as Hermione had planned it.

"Give those back," she said, trying to sound as petulant as possible.

"What?" Romilda looked bewildered. "I'm not giving them back. What are they?"

"Romilda, they're my favourite snacks. Give them back, now. See, in Hogwarts: A History, Godric Gryffindor used chocolate-covered nuts to..."

Romilda snatched the nuts away from Hermione's outstretched hand. "Well, they're mine now."

"Don't you dare eat them!"

"I think I will!" Romilda shoved a handful of nuts into her mouth and handed the packet to Parvati, who promptly did the same. Lavender followed suit. "Come on, Hermione. Just because you know Harry Potter doesn't mean you get to... eeeeeEEEEEEEK! EEEEK EEEK EEEEEEEEEEKK! STOP! DON'T LOOK AT ME!"

She sprang into the air, waving her arms around, too overcome with sudden shock and embarrassment to think rationally. Lavender sat still, frozen in place, her mouth partly open, completely unable to move, while Parvati squealed and tried to curl up into a little ball. All three girls had suddenly been stripped completely naked, and they didn't look happy about it.

Hermione allowed herself a little smirk of her own. She might not have any pants on, but at least she didn't look as ridiculous as those three.