i'm so upset right now...

I would call a behaviorist, growling is not acceptable and your dog needs to be trained to be more comfortable in those situations.

Your brother deserved it, though.

Dogs get sick too.

First the dog warned he was not feeling weel with the growl
and you never put your face into a dogs face without reading the dog wanting a kiss.

He may have a bug.

Hope things do well.

IF I told someone to back off once and then they went to kiss me I would of punched them too.

ADDED do a thyroid panel at the vet it could be offer very common for all of a sudden aggression.

Aww I'm sorry Milo, let us know what the vets say.

The thing about getting in a dog's face being a good way to get bitten ... I cuddle and hug Skye. She will elect to lean on me in the sofa and twist her head up and back to look into my eyes. Playing with her I will grab her jowls and play kissy, kissy right in her face. BUT she's my dog, I've had her for 6.5 years now and we're both comfortable with that. I wouldn't encourage my kids to do it though and don't play with Skye like that when they are in the room. Not because Skye would react or be uncomfortable with them, but because I don't want them thinking that this is the way to play with a dog and trying it out on any dog they don't know.

alot of times a very sudden onset of agression is medical based, have the vet give him a good physical, especially if this is not normal behaviour for him. dogs cant tell us when they dont feel good, growling is often theri way of saying ok enough...
think of it like pms, how much can you take before you finally just snap at someone.
get him health checked first before jumping to any "oh my dogs agressive" problems.

if the vet gives him an all clear after a good solid physical (a blood work might be worth it if nothing shows in a simple hands on) then it would be best to find a good behaviourist/trainer in your area whos expereinced with "quick change" dogs.

this to me doesnt seemlike typical "agressive behaviour" it seems like likely to be a something is upsetting me kind of behaviour.

good luck!

I put my face in my dogs face all the time. We love to give Eskimo kisses. However...my dog is not actively growling at me while I'm trying to do this! That's a pretty clear signal to back off, buster.