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Yashur, are you referring to Special Relativity?
The idea of Special Relativity is the universality of physical laws in inertial frames of reference. This (and how this universality is achieved) solved problems with Maxwell's equations, for example. Something like that.
Two objects... What example can be used to illustrate this principle? An apple and a forehead? A dent in the apple, a bruise on the forehead... Regardless of the frame of reference, it still hurts. It's not trivial at all.
If the idea is about the constant speed of light... That doesn't quite fit either.
If you mean General Relativity... Oh, there Einstein did some recalculations, refined the orbits of planets, and this confirmed General Relativity very well at the time. But it's unlikely that non-physicist friends would understand anything about the refined orbits.