Language is a funny thing, it can be translated, miss interpreted but most importantly altered.
Through slang or plane randomness, alterations are made. 
Here are a few I know. 

"Yes" or as we now say "YEEEEEEEEEEEEE"

I'll admit, we all started saying it to be ironic but somehow it's stuck.
It's more fun then just saying yes but when you go to a job interview and they ask you a question, 
to which your response is "yeeeeee", suddenly it doesn't seem like such a good word....

"Friend" or as we now say "bro" / "brah".

It's saying you're such a close friend you're like a brother.
That's kinda deep so lets focus on brah.  
Abbreviation tend to be shorter so why did we add an extra letter?
Admittedly "br" or "ro" sound a bit stupid...
Also brah is a fun word to say, especially when you say it braaaaaaaaaaaaah. 

"Thank you" or as some people say "safe"

This is a bit more London chav language but it's somehow managed to stick around.
Personally, I hate the word.
Gives the impression that you were in some form of danger unless you done
something for the person that required thanking.

Do you think these words stay changed? 
I'm on a personal mission to make abolish the word safe.
To be fair films have taught us safe is just a word used to emphasize a fake
sense of security so I wouldn't miss it is it disappeared form the dictionary.
How many films have you watched that someone has said "we're safe" 
then they get vaporized by aliens? 

Alright, back on topic. 
Do you guys know any words we've replaced?
Comment bellow and as always;

Thanks for reading,
Mario El