According to Osho, you react instead of laugh because conditioning has labeled natural realities—especially sex—as “dirty,” so jokes touching those areas stir repression, guilt, and fear rather than playfulness. An innocent mind sees nothing obscene. By witnessing your reactions, dropping borrowed moralism, and accepting the body’s naturalness, the charge dissolves and laughter returns as a spontaneous, healthy response.
Those jokes hit old, learned shame about natural things, so you tense up—notice it, relax, and laughter will come.