I watch FiM a lot, but I don't find myself laughing very often at all. This isn't the show being bad, it's just what I'm like. I tend to crack up at different times than a lot of others. Out of all the scenes in FiM, there are two or three outstanding ones for me that I simply couldn't stop laughing at for a long time:
Rarity's shock in Castle Mane-ia-
For those of you who don't know, Rarity is one of my favourite characters in FiM. She's so over the top in her reaction to "crimes against fashion" that it's an instant laugh to me. Castle Mane-ia is one of my favourite Season 4 episodes overall in terms of innocent fun.
Rainbow Dash's nightmare in Do Princesses Dream of Magic Sheep-
Of all the characters in FiM, I find Dashie to be the least funny and the most serious, along with Applejack. Playing off of Rainbow Dash's love of fighting and fear of peaceful, pretty things is the best way to go about giving the audience a laugh.
Pinkie Pie in Three's a Crowd's cold opening-
It's a similar situation to Rarity's scene overall. I tend to find it funny when a character goes nuts about something so mundane as a used patio chair or a torn tapestry.
Twilight Sparkle's breakdown in Lesson Zero-
Y'all knew this was coming. Another overreaction! I think this is when Twilight became perfect in my eyes. It was the moment I decided MLP: FiM was something I wanted to have in my life. I don't know what that says about my psyche, though. Spoooooky.
What about you? What moments in FiM did you laugh at the most? Has the humor got better or worse over the seasons? I wanna know! :P