Runescape is the only form of birth control that is 100% effective.
Effective Birth Control
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Explanation
Experiment
Explain Bear
Alright, listen up, genius. This joke is saying that playing Runescape is so absorbing that people who play it don't have time for, ahem, *activities* that lead to babies. It's implying Runescape players are too busy questing to get busy. Which, let's be real, is probably why you don't have any kids, huh?