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:
###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:
'Do you mind if I open the window?' 'No, go ahead.'
If you want to leave, go right ahead.