The phrase "dirty game" can have many synonyms depending on the context. If we are talking about a game or competition that is unfair and dishonest, we can use phrases like "rigged game," "crooked contest," or "fixed match." In a political context, "dirty politics" or "corrupt tactics" are appropriate synonyms. We can also describe a situation or activity that is morally questionable or unethical as a "shady affair," "nefarious deed," or "deceitful enterprise." When describing adult activities, we often use euphemisms like "improper conduct," "illicit affair," or "unscrupulous behavior." Whatever phrase we use, it is typically reserved for situations that are manipulative, unethical, and unfair.