A person (usually a man) who succeeds in busting a nut, 100% of the time when he engages in sexual activity. This is a term of high regard, and connotes that one has the sexual prowess to effectively release their load 100% of the time during sexual relations. Also known by the acronym GC'er.
Hey Kristen, I'd love for you to meet my friend, he's a great guy, a real mensch. Like all of the stallions who I call my wingmen, he is a Guaranteed Cummer.
What do you mean a Guaranteed Cummer?
Oh, he cums every time, 100% of the time!