Shaving, brushing my teeth and freshening up is a standard routine on my monthly transatlantic travel in LH C or F. Basically, I'm doing my standard morning bathroom routine from home, minus the shower of course.

In eastbound F, the final bathroom visit also involves changing back from the airline's PJs into street clothes.

I can't see why any of this should be a problem, after all, the LH F lavatories are filled with one-way shavers, shaving gel and after shave, mouthwash, toothbrush/toothpaste, face and hand moisturizers etc. This stuff is obviously meant to be used and so far, I haven't encountered any problems with impatient pax. ^