According to Osho, you should remain true to your actual feeling - even if the other is radiantly positive - because only truth meets truth. Mimicking another's laughter or 'positivity' is a lie that blocks communion. Authentic expression lets repressed energies release and naturally move toward balance and inner silence. If forced to choose, prefer the positive; but higher than both is tranquillity born of sincerity.
Yes—be honest about how you feel instead of copying their positivity; real connection happens when both are genuine.