A common lie is that I'm in a relationship with my "girlfriend". In truth we just live together in a flat, spend some time together for some needs, but are otherwise independent persons. If i say we are together, people draw wrong conclusions. If i say we are just flatmates, people draw wrong conclusions.
With people projecting their own ideas of the world onto everything, truthful talking stops being useful. So i fall back to replaying some common stereotypes so people don't bother me anymore and let me do my own stuff.