What's common in the MMDC:

People stealing other people's work and not crediting.

Me:

*Event 1*

Random person: Did you do that?

Me: No, this motion was made by *insert original creator's name here*. I just downloaded it and loaded it onto my model. I'm not that good at animating yet.

*Event 2* 

Random person: Did you make that model?

Me: Not exactly. I used parts made by other people and put them together. It's stated in the credits.

*Event 3*

Random person: Nice model you got there!

Me: Thanks but the model belongs to *insert original creator's name* so be sure to tell them that.
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Some things I'm paraphrasing but this did/does happen to me XD;; Mostly with followers on Twitter/Tumblr/my main Youtube account. Oh and teachers/students at school to. And my dad. And some friends.

It's hard trying to explain the works of MMD to other people who've never heard of it. XD;; 

That's why I put the 'I DID NOT MAKE THIS MOTION!' in my videos where I used someone else's motion.