[What](is) this blue line.....

It means you need to stop touching yourself at night

Really I have no clue

Let it load and it disappears

Why is the sky blue? Why are dogs cute?

I was wondering this also, but I assumed it was something with the Developer Giveaways. As of now there is 'Faerie Solitair' running, and since we both own it, I believe it is plausible.

It shows it when you have the games for the developer giveaway.

It's all in your head. It'll go away with time.

Victoria line.

All the dev/featered giveaways are filtered, so that's what you see.