Six times Arya caught her siblings in compromising positions (and the one time it happened to her)

Sansa

The first time is a surprise.
Arya is nine, she has just arrived home from her first weekend away with the Cubs and she hasn't seen her family for so long she fears they might have forgotten her face.
It isn't as though she misses them, she is almost ten and therefor very grown up, but she is quite excited to see her mother and father. And very excited to see her half-brother Jon. And her 'real' brothers Rickon, Bran and Robb, and even her sister: stupid, annoying Sansa.

The second her father opens the front door, she bolts up the stairs, taking them two at a time. Arya and Sansa's shared room is to her left and she pushes straight into it.

"Sansa, I'm home!"

Her sister isn't alone in the room.
Instead, a boy, probably ten-and-four, sits cross-legged on Sansa's bed, his back to Arya, but she can see he is leaning forwards, lips pressed against-
"SANSA?"

Sansa whips her head up, eyes wide as saucers, the boy turns away and Arya recognises his fat, wormy, pouty lips.
Joffrey Lannister, her boyfriend of only two weeks.

Sansa's cheeks are as red as her hair as she screams at Arya to leave them alone, Joffrey is yelling to, much more angrily.
Arya doesn't hesitate backing out of the room, watching her sister kiss horrible, rich boys isn't something she wants to do.