When the whole team slacks off, be the one who still runs the full lap. People notice who stays solid.

Standards belong to a person, not to a group. Running the full lap when nobody else does is not about being better than them, it is about not handing your own decisions over to whoever happens to be standing nearby that day. People notice quietly too, and they tend to remember who stayed solid at the point where it stopped mattering.

Decide what you do before you arrive, so the room cannot vote on it. Do your version without commentary and without looking around. Let the difference be visible rather than announced.