Big Paws Only Dog Forums

Hi all! Thank you for welcoming me into your group! I read a few posts about peer pressure to add more babies to the family lol. Well I am all for that once we get moved to a farm someday. Right now we are in a small town in a small house. We have been lucky but many of our friends have had neighbor problems. I did one day, as I was in the house Loki got loose, I was right behind him in my pickup but that didnt stop this man from whipping his car to the wrong side of the road (diagonally parked on a residential street) He started running and screaming at my dog then at me about him not being on a leash. I tried to explain that Loki was properly leashed or confined almost all the time but that all dogs get loose, he did not care, he scared my poor baby. And seriously I was angry, I think that if he did not want the dog around him then he should not get out and chase him (it was not his yard)It was very frustrating. I have neighbor dogs in my yard all the time yet this once my baby gets loose and i get in trouble. But that is not the problem today, my problem is weird. I have a very well socialized dog, he plays everyday with neighbor kids, comes to the nursing home i work at regularly and the residents love him, I have seen him try to play with other dogs before that get upset with him becaues he is big and playful. He is about 90 lbs, 1 year old. He had always been very friendly with other dogs even if they get cranky with him but today he met a 13 week old rottie and snapped at him several times. I don't know, maybe it is normal, and they would get along eventually but I have never seen him act that way before towards anyone, any animal, not even cats after getting smacked. How can I stop this behavior before it gets out of control? Or is this something that will probably not be a big problem? He did not bite, just got grouchy and snappy, snarled a bit.Otherwise he has always been well behaved, not even getting into trash or eating shoes, very happy puppy. Any advice is appreciated.
 And do not worry, He was not trying to eat the kids in the following pics lol, this is his daily activity, Everyone has a blast.