"Unspillable" Mug Carrier

Every morning I carry a big ~0.4-0.5l mug of coffee up a flight of stairs, while sleepy and in the dark and I spilled it one time too often!

Sadly the model I took heavy inspiration from was not big enough for my mug and it was not prepared to print in its strongest direction with minimal supports.
I recreated the rough shape in fusion 360, split it in half, to have the layer lines correctly oriented towards the stress and added some dovetail joints to fit the model together without glue, which worked surprisingly well on the first try.

I would STRONLY advice PETG or a similar filament, because most people will carry hot drinks with this and it has some give like it is, PLA would most likely bend under the combination of heat and stress.

Also: If you fill your cup up to the brim, like I often do, test the balance first, because if you're not perfectly centered, your center of mass might be off and you end up with a stable, but slightly crooked angle.

And don't be frightened, because it hangs slightly off while empty - that's the arm's weight. A properly placed mug should counter that when placed correctly.

Assembly:
There are two straight dove tail pieces, that should be flat and interchangeable (printed sitting on the face) and one that's slightly curved (printed sitting on the side). The flat dove tails go into the dish at the bottom and the curved one goes into the arm. You should be able to press-fit them in with strong fingers or delicate use of a non-scarring set of pliers. You can add glue, but I was happy with it without any glue.
Lastly thread in a closed loop of thread/yarn/cord from below until the bight sticks out above, wrap the rest around the arm and thread it through the bight loop front to back (aka towards the arm). Like this he CoM gets shifted back a few mm and the cord helps to keep the two pieces tightly together while preventing the cord from slipping out.