according to my vdict:

dạ - yes; please
vâng - yes; all right

and according to my dictionary:

dạ - [polite particle] yes! (I'm here, I'm coming, I heard you); yes, you're right; yes, I'll do that; no, it's not so (you're right).
ex. ba gọi sao không dạ = Father called you. Why didn't you answer?
ex. anh không đi à? dạ = Aren't you going? No.

vâng - to obey; vâng loi - yes - you are right; yes, I agree [it is so or it is not so]; [polite particle; not used to answer a yes-or-no question]

ạ - [polite particle used by child to elder, by inferior to superior] vâng ạ - yes, sir.

gọi dạ bảo vâng - to say dạ when summoned and vâng when told something

and according to my mom, she would only respond with vâng ạ to someone her parent's age, or only to be extremely polite.

i understand all that, but what about using it with someone your own age? say a friend or girlfriend/boyfriend for example? does it have any connotations or implications? have you ever witnessed this? in real life? on tv? what about regional differences? and what does dạ vâng mean exactly? what goes through your mind if you heard someone answer this way to a friend that is the same age?