***Go ahead*** is something that I hear pretty frequently these days. It mightn't be very formal, but it's not negative anyways.

From [LDOCE][1]:

> ###**go ahead** 
> *phrasal verb*
> 
> **1**	to start to do something, especially after planning it or asking
> permission to do it:
> 
>- ***go ahead and do something***  
>*I went ahead and arranged the trip anyway.*
> 
> 2 ...
>
> **3** *spoken* used to give someone permission to do something, or let
> them speak before you:<br/>
> *'Do you mind if I open the window?' 'No, go ahead.'*<br/>
> *If you want to leave, go right ahead.*



  [1]: http://www.ldoceonline.com/dictionary/go_1