Toby is usually such laid back, placid boy but this morning he snapped at someone for no (apparent) reason. We were on our usual walk, turned a corner & a man who we have seen before was dragging his wheelie bin to the side of the road. It was dark(ish) but it's not as if he suddenly appeared. He stood & chatted to me, he is a bit odd but not scary & Toby was wagging his tail in a really friendly way (not low & slowly) & kept sniffing him. Then once he's sniffed him a couple of times, he suddenly growled & went to snap at him. It wasn't an attack or anything overtly aggressive but a short growl, ears back & a sort of small lunge followed by a snap. I made Toby sit down & then he growled again & barked at the man. I found myself apologising & usually the cliched old line 'he's never done that before' .... but he hasn't. He is usually such a friendly dog & wants a fuss from everyone. The only time he has ever been aggressive (ish) towads anyone was when a cyclist suddenly appeard from round a corner, it was really dark & I really jumped. Toby was instantly by my side & growled at the man but that was an understandable incident. In this case there was no sudden movement, no fear on my part, the man did not move to stroke Toby or act in anyway that would cause him to be scared/nervous/defensive/protective (as far as I could tell). As Toby is a reasonably large dog (Lab/GSD) so this is a worry as a bite could be serious. This may only be an isolated incident but I don't want to ignore it in case it happens again & I am confused why he reacted like this. Sorry for the long post & I know that unless you were there it's very hard to determine why this happened but any thoughts would be really appreciated.