I felt this thread should be made, so I'll discuss the difference between the two:

When giving someone advice, you should use constructive criticism.

Giving someone destructive criticism is, on the whole, not appreciated in these forums.

Help build eachother up rather than discouraging or knocking eachother down

-Arc

EDIT:

A second point I'd like to make is in respect another user's style/preference in method (This is mostly in response to anti-Minemator comments). You may (politely) suggest a different way to get from Point A (the beginning) to Point B (a finished product), and you may support your claim of how Method B may be more flexible or more efficient than Method A, but when it comes down to it, it's a creator's choice on what method they would like to use. As with criticism, one should not just say that a program "sucks" or tell a person to flat out stop using a certain program. One should suggest or offer advice but  not demand.

I agree, it is important to understand that people will take your opinions seriously.

Making unhelpful and/or negative comments offends others. 

If you don't have anything to say that is helpful, I recommend to not say anything.

People may not always think, 'oh someone said my creation is bad, is there something I could do to improve it?"
Often, this sort of sentiments is created, "oh that moderator says my build is bad...I'm pretty bad at this.."

This doesn't just apply to the forums/server, this applies to your real life.
If your friend/colleague made unhelpful comments about your creation you worked hard for, won't that make you feel down?

Thanks for the post Arc. Please be careful of what you say/write, everyone.

0_0...oops. Some people has some language to work with helping others...

I feel as though this was made because of my TARDIS design.

 Don't blame this on you man its not your fault this happend. People just need to be more carefull of what they saying. You did nothing wrong.

 I'm not.  I'm actually somewhat honored.  I was kinda taken aback when i saw this post, and when I read it in-depth, I got the feeling that i influenced this post.  I was actually surprised I had that kind of influence on this part of the forum.