Dinner time:

Me: *sits down to eat and starts eating*

After a while:

Me: I need water.
*extends hand toward the jug and brings it close*
*looks at my mug half filled with water*
I guess that water is not clean. But the place to clean it is too far.
*looks behind at the cleaning place just behind the chair*
Sigh...
*pours that water in big bro's mug, then again does it*
*then drinks from my mug*

Big bro: *comes and drinks water placed in a mug beside me*

Me: *looks at my mug*
Huh? If my mug is full, then the one he just drank is...
*looks at the empty mug where I poured the probably-unclean water*
*facepalms*
I don't think that water was clean.

Big bro: Then why did you keep unclean water in it?

Me: Σ(￣□￣)！
You've gotta be kidding me. How did he know it was me?