What does it REALLY mean when a girl says, 'GROW UP!!!'?

[martyfellow]

It's usually a code for something she wants, but doesn't want to say in so many words.

[idk87]

your making her nervous or you really do need to grow up could go either way I've said it when I was nervous around a guy if he was teasing me and I've said it when a guy was really being immature

[Paris13]

... Here's a quarter, call me when you are Adult enough to talk to me...
Right on the money, for I have used this myself in my own life, believe me. xx

[Genie23]

Umm.. I guess she meant don't be so stubborn/be serious

[Genie23]

Never said that to anyone, lol

[I_M_LEGEND]

it just means theyre not getting their own way.

they use this interchangeably with calling them losers.

they are control freaks often once they get inside.

[martyfellow]

Not one girl would admit that it is usually a coded phrase, with more or less the meaning you suggest.

[Theguyoverthere]

Either you're being immature, or you're not giving into a demand that she wants. Really depends.

[ironeddie]

It means. You're acting immature. It's time to be an adult

[lanagirl]

She thinks you're being immature. That's the only reason I would say it.

[AkumaKira]

It means what it looks like. Stop acting like a child.

[madhatters4]

it means that they girl thinks you could use some maturing.

[Prof_Don]

Pretty much that means "you're not handling your adult responsibilities"

[douride2]

I would say the meaning of that phrase is pretty straight forward.

[martyfellow]

Not usually, no!

[Luvme66]

Come on dont be selfish and get me something!
Maybe this is it! Lol

[Kshppatel]

You're too short lol jk but it probably means you are being childish

[abundantlyrich]

It means stop fooling or fucking around.

[martyfellow]

They'd just SAY 'stop fooling around' if that's what they meant, right?

[abundantlyrich]

Another meaning is get smarter, please... :P Stop being stupid.

[DontDropIt]

I usually say it in a joking manner.

[zombiebabe]

it means she really wants you to be serious

[jacquesvol]

She thinks you're acting in an immature way.

[miss_ana]

She want you be more matured