Are you thinking of "bloody murders" (common in crime fiction or horror) or perhaps "bloody Marys" (the cocktail)?
This may be a fragment from a specific conversation, a niche piece of media, or a slight misremembering of a similar phrase. Here are a few possibilities to help you find what you're looking for: bloody matures
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. Are you thinking of "bloody murders" (common in
(e.g., a movie, a social media post, a book)? Any other words from the sentence or surrounding lines? a niche piece of media
Whether you think it's from a (like British or Australian English)?