"Semantic satiation" is the phenomenon in which a word loses its meaning after it's constantly repeated. It applies to any word, really, but is especially true for profanity. When it's used well, it adds humor or proper shock value. But most times, people just use it for the sake of using it, which is absolutely pointless. What separates a subversive garment from a novelty sidewalk souvenir tee is some nuance.