When I was 15, my mom thought I was starting to head down the wrong path in life (spoiler: I was) so she made me attend our Lutheran church's youth group.
It was only an hour a week - no biggie. I didn't really believe any of it but whatever - you put up with that type of thing when you're a kid.
As many may know about Lutheranism, it's a very "Sunday" religion. They're not all fire and brimstone and guilt and penance and whatnot. You show up on Sundays, sing some horribly boring songs, maybe eat some donuts or something, then gtfo.
So 2 months prior to this event, my grandpa died of prostate cancer. I was pretty bummed cuz my grandpa was rad. And it just so happened our "lesson" this day dealt with heresy which led into the discussion of how our particular branch of Christianity was right and all others were wrong....which led to the question of where all those other people ended up...the answer being "Hell".
I didn't really participate in discussions usually but my ears perked up at this and I said " whoa whoa whoa...wait a second." The pastor, (who in retrospect was a pretty rad guy but whatever), looked at me like "oh fuck."
I said "Important question here. My grandpa was one of the best people I ever knew. He was an entirely selfless person who lived to make other people's lives better. He founded unions. He lied about his age to join the navy at 15 and be a cook because he wanted to stop Nazis but refused to take a life. People speak of him as a saint. Speaking of which, he was Catholic. He wasn't practicing, but he was raised Catholic and that's what he believed. He's been dead dead months. Where do you think my grandpa is right now?".
My pastor looked down and mumbled " Well, it's uncomfortable but the church has teachings that say...well..."
I, in my teenage defiance, stood up and said "No. You say it. My grandfather. My father's father. Where is he right now."
My pastor looked at me with sad eyes and said "Well, we believe he's in Hell, son."
I looked down, sighed, looked back up, held out my arm, extended my middle finger, and proceeded to go around the room saying "Fuck you" to every kid in the class and ended on the pastor. Stuck my finger two inches from his face and said "And especially fuck you, you fucking monster. I'm done with you and I'm done with this bullshit building and your bullshit books and your bullshit opinions. I'm gone forever."
I walked out of the church and by the time I'd walked home, he'd already called my mom and "explained" the situation. My mom was in near hysterical tears. I told her "No. I don't care. They're bigots. Fuck them. I'm done." (It was the first time I'd ever cursed in front of my mom so that was a rush in and of itself.) And I never went to church again.
I've been what you could call an agnostic atheist ever since. The reason I regret this is because it destroyed my mom. Me leaving the church was going to happen sooner or later, but it didn't need to happen in such a dramatic fashion.
18 years later, I still get kind of a rush when I think about it though.