Some games are just hard to play around people, perhaps Kirby's cuteness makes it one of those. Strangely I never came across the issue with LBP even though that game is abnormally cute for the platform, but that's mostly because the only people around me that would make fun of me are also gamers so they would play the game with me and quickly shut up, I suppose you could try that with one of your family members to see if the inherent fun of the game stops them from deriding it.
Personally I've only really been made fun of by my friends while playing some of the more nichey Japanese games with ridiculous stories like Eternal Sonata (watch the final cut scene to that if you have the time and brain cells to spare one day) and ToS2 or more pervy games like Ar Tonelico 2 because it's just embarrasing when your main character keeps yelling "MAXIMUM PENETRATION" whenever you do his best attack.
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