Beelzebub
Sypnosis: Serialized in Weekly Shounen Jump in February 2009. The story is about this invincible delinquent who found this mysterious baby by accident and the baby became attached to him. It turns out the baby is in fact the next Demon King in line and now Oga Tatsumi (the main character) is chosen as his parent. Burdened with the responsibility to raise the kid while avoiding the kid to grow up to a demon that ends all mankind, what kind of trouble awaits the legendary Oga?
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Only 3 chapters are out so far, but it's absolutely hilarious. I was sold from the first chapter and haven't been disappointed yet.
Also, there was apparently a one-shot version of this manga in one of last year's Jump Issue.