Synchronized Morning Routine

A scene where two characters are washing up in tandem, and which includes them brushing their teeth and gargling while facing the mirror. Is generally presented as a cute scene, and the participants can range from relatives, Heterosexual Life Partners, those potentially in a romantic relationship, to romantic partners. Usually played as humorous.

Sub-trope of Morning Routine.

Examples of Synchronized Morning Routine include:

Anime and Manga

One episode of The Melancholy of Haruhi Suzumiya begins with Kyon and his sister doing this.
In Ichigo Mashimaro, a flashback shows 6-year-old Miu popping over to the Ito house to leave her wet undies and bedsheets and comes in on 10-year-old Nobue and her 6-or-7-year-old sister Chika brushing their teeth. It is cute, but that's not surprising.
This is part of the Training Montage in which Shinji and Asuka learn how to move in synch for a Monster of the Week in Neon Genesis Evangelion.
All three Paper Sisters do this in Read or Die. They think its cute, Nenene thinks its just creepy.
One of the openings for One Piece had the entire crew doing brushing their teeth together on a hillside.

Film

Torrance Shipman and Cliff Pantone in the movie Bring It On.
Doug and Steve in A Night at the Roxbury.

Live Action TV

Seen in Frasier.
Lorelai and Rory in Gilmore Girls have their routine.
Morecame and Wise's breakfast routine, set to the tune "The Stripper".

Webcomics

Kelly and Julian did this in a recent The Wotch.

Western Animation

Wallace and Gromit have a rather elaborate approach to this.