Just a very short one shot. Set during OoTP, maybe summer, maybe Christmas. You decide.
"Have you ever noticed the way Tonks holds her tea?" Remus asked Sirius one day. Sirius looked up from the Daily Prophet with a frown.
"Have I what?" He asked, staring at his best friend.
"Have you ever noticed that she doesn't hold the cup by the handle? She instead holds it like this," Remus picked up his empty cup and copied what he had seen Tonks doing earlier. He slipped two fingers into the handle, his other finger clutching the cup itself. "Have you seen it? Never seen her spill any of it, even though she's knocked over how ever many dishes around here-"
Sirius stared at Remus for a minute more before breaking into a grin. "I have a feeling there's more to this than you being fascinated in the way Tonks holds her tea."
"Why would you say that?" Remus asked.
"Because I can guarantee- no one else has noticed that." Sirius said.
A few hours later, when Sirius wandered back into the kitchen before the Order meeting, he found Tonks looking over some parchment. In her left hand, she held a cup a tea. And with a grin, Sirius noticed exactly what Remus had said was true. There was a way to use this to his, and possible theirs as well, advantage.
Just as she took a sip, he walked up to the table and announced loudly: "So that's what Remus was talking about earlier!"
She jumped, dropping the cup and choking on her tea. Through spluttering coughs, she glared at her cousin. "Sirius- what- the- actual-"
But whatever she had been about to say was cut off as Molly and the kids entered the room. Tonks set about clearing up the parchment and spilled tea quickly.
"Oh, Tonks, did you drop another cup?" Molly asked naively, hurrying to help with the clean.
With a glare at Sirius, who was trying to hide his laughter, Tonks answered Molly brusquely. "Yes, I suppose I did."
I just like the idea of Sirius having fun at the expense of other Order members.