(e.g., a movie, a social media post, a book)? Any other words from the sentence or surrounding lines?
In British slang, "bloody" is often used as an intensive. "Matures" could refer to a specific group (e.g., "Those bloody matures are at it again"), though this is not a standard idiom. bloody matures
Are you thinking of "bloody murders" (common in crime fiction or horror) or perhaps "bloody Marys" (the cocktail)? a social media post