Call him 'beaky'
If there was something Snape loved more than taking points from Gryffindor students, it was putting them in detention. Especially these two. The Weasley twins, Fred and George. They sat before him in the empty potions classroom, writing out 'I must not explode my cauldron on purpose'. Or at least, that's what it seemed like they were doing. Snape lifted his head briefly from his marking to find them whispering together.
"You two!" He snapped, and they turned around to face him. "Stop talking and get on with your lines this instant!" They beamed at him in that disturbing way that they had, and chorused,
"Yes sir, beaky, sir!" Then resumed writing. Snape paused, then shrugged. They wanted him to say something about it, he could tell.
When the time allotted to their detention was finally up, Snape gathered in the papers he had been marking.
"You may leave now." He said coldly.
"Thank you, beaky!" They replied in tandem, and left the room. As they left, Snape growled softly to himself.