IRREGARDLESS IS NOT A WORD

Despite what you read and hear, there is no such word as irregardless. 

The proper word choice for what you want to express is regardless. 

For example:  

Regardless of the circumstances of your leaving, your first responsibility is to inform your employer that you are resigning.

IN BEHALF OF or ON BEHALF OF?

What is the difference between in behalf of and on behalf of? 

In behalf of means "for the benefit of" or "in the interest of."

For example:  The First Lady hosted a charity dinner in behalf of the street children of Metro Manila.

On behalf of means "in place of" or "as the representative of."

For example:  On behalf of the President, the First Lady thanked the people for their loyalty and support.