I'll admit that the Birthday Song is fun when you're a kid. It's only trolling when you're of a certain age, especially an adult. And mainly because you get that fun "you're gonna die" tie in with it said to you by people who supposedly love you with as much sarcasm as possible. E.I. what the "Over the Hill" gag gift industry exists/lives for.
Luckily, I'm not quite in the hilarious reminder of death inflicted by friends and family stage yet. But that's where the Happy Birthday song goes from cheerful little greeting to sarcastic, snarky, "we're your friends, so we can call bullying 'teasing' and get away with it." Seriously. What the heck is the deal with that?