Most people have semi good grammar, so this should be a nice little fix. When you type, you usually use spaces. Ex:
Bob says:
Hey John, I g2g, hospital time... 

---> Hey John, I got to go, hospital time... 
 
John says:
Okay, br buddy 

---> Okay, best reguards buddy 
 
So, a simple fix would be instead of:
sMessage = sMessage.replace(/br/gi,"best reguards");
make it
sMessage = sMessage.replace(/ br /gi," best reguards ");

. Notice the space. This wont catch "br" at the end of a sentance however. But if you put an extra space at the end, it'll catch it 

.
This is how I wrote my personal script anyway.