It can be canon or not. To me, it was when Spike declared his love to Rarity. Also the "I'm Octavia" song.
Hmm, a lot of things I guess. I'll just give the happiest moment and saddest moment that made me feel feelings about stuff. Saddest moment: Like a lot of others, when Twilight became corrupted due to Discord manipulating the others to become their opposites. It was surprising to me at the time, and it was just as bad as if I had to watch her get killed. Happiest moment: When Twilight found the real Cadance in the cavern. We were all on Twilight's side at the time and I'm sure our reaction was the same as hers when she shattered the wall. You know "I'm gonna tear you to pieces." Then Cadance began to explain the situation and I'm thinking "Oh you tricky b****. Give it a rest." Then when she started doing that old dance of theirs, well....yeah....emotions and whatnot.
The Show never made me cry, though I've gotten a bit watery eyed from time to time. ... I suck. xPPP I think the last time I cried waaaas.... My Little Dashie. Yup. About 2 years ago, I do the believing of.
My little dashie was sad. I was shaking afterwards but it was so good. ;-; Also, when Fluttershy got corrupted, I died. That was so cruel. How could you do that to Fluttershy? FLUTTERSHY. ;____; That was so sad. I actually got worked up thinking about it. xD *is 20* I think my happiest moment is also in order now that I think about it. This moment was when True, True Friend was being sung and Pinkie Pie realized what her talent was. It was so perfectly timed. I get goosebumps every time I hear that song now. COME ON PONIES I WANT TO SEE YOU SMILE! PINKIE! She made me smile. I couldn't help it. ;-;
The closest I came was when I read My Little Dashie. As far as canon, I've never cried but I do get a little perturbed when somepony makes Fluttershy cry.