Is it normal to make a grammatical error on purpose for the way it sounds?

The English language is illogical most of the time anyway. What matters is that you get the point across.

As long as you recognize what you might say in common speech, is not how you would 'normally' write (there are exceptions, notably when building character in a story).
Also, it is important to recognize when you are in a formal or informal situation.
The trick is to sound natural in all situations.

I do the same thing in a informal situation. Normal.

To you it may sound snobby, but to people who use proper english probably think you sound ... like something else.

I do this frequently. I think it is natural to speak the way you most often hear others speak. Unfortunately, you should think about you audience. I grade grammar tests in an engineering department. I am not an an English major, but I have better skills in this area than most engineering students. Last month, I was in the office of the professor for whom I work, and I caught myself saying, "me and my friend..." I was so embarrassed. I also agree that correct grammar often sounds pretentious. I cringed when I wrote, "the professor for whom I work." It also would have bothered me to write it incorrectly!

Me and I do this stuffs too

I like using old timey sounding stuff like "fornicate thineself".

I do this too, it just sounds better!

There's only one way to tell girls suck my cock. That's probably why that rich English chick I tapped didn't doubt my intelligence.

In Spanish there are several examples like this, where you feel much more comfortable saying it wrong because you never hear people saying it right colloquially, so you know you'd sound pretentious if you did.

Oh my "gawd"

I do this all the time to a much more egregious degree.

I do that too. Instead of saying "may I go to the bathroom", I say "can I go to the bathroom... But I'm not sure why I do.

Yeah it is. In my case, I cant help using !, all the time!

normal. Also some things that are right sound incorrect eg: He was hanged. It bothers me that its not hung

Yeah, but I wouldn't use it in a CV or formal document if I were you.
In our university, they actually encourage us to say "one" for "I".
E.g. "One wanted to increase the piano volume, but prior gating meant one had to reconfigure one's previous creative decisions."
It's kind of creepy, especially me being a ghetto boy...
In fact I find most people at Uni a bit too posh...
But yeah, totally normal to feel that way, as long as you don't let it affect your career.

Grammar rules are just there as guidelines for a set standard so that when someone is in a formal setting they know how to behave.

Written English and spoken English are surprisingly different animals. Say "finger." Now say "singer." Now say "ginger." They look alike, but they don't sound alike because spoken English is nutty.

I say "Anthony and I," but I don't bat an eye at "Me and Anthony" in speech. Plenty of people say it, and it often has a better rhythm. You'd best believe I turn hostile when I see it written that way, though. It brings out my inner Conan the Grammarian.

Maybe but not just to get people mad tho.

This makes me feel like i need to learn english again.