Chihuahuas are assholes and will go after anyone even if they were invited. As a delivery driver who encounters a lot of loose dogs - and some leashed in the front with reach to the door - it's the chihuahuas that will sneak up behind you to bite you. But they'll run off if you confront them, yapping the entire time. Had some cowdogs, lab mixes, etc be aggressive and act like they might bite but didn't. Usually growl and bark as you move towards the house then are fine as you go back to the car. But I keep the package between us just in case. Only had one - a pit - that was chained up in the front that I decided not to tempt fate and just left it on the car in the driveway. Super aggressive and I didn't want to provoke her more and worry about that chain coming loose. Plenty that were behind fences or gates that would've killed me if they could've gotten to me. Had a German Shepherd the other day that was trying to chew through a metal mesh fence to get to me. Had many different breeds and sizes test the glass integrity of front windows. And nothing gets the heart beating like bending down to put a package by the door when the THUMP of a huge dog hitting the other side at full force and no prior barking scares the shit out of you. Had one cat try to attack me. One peacock walked around the side of my vehicle and suddenly appeared right by my knee and made me jump. A buffalo refused to move out of the middle of a long driveway and I just went back out and left it at the gate. And once I walked up to a country house to leave a package, turned around and a horse was standing at the bottom of the steps. Never saw or heard it until then. Another driver was delivering in the early morning dark a couple months ago and opened a gate to a yard to leave a package at the front door and was attacked by a dog - a pit mix - and had to get 22 stitches to his arm and leg. No "Beware of Dog" sign and the dog didn't bark first. I don't even bother going into fenced yards in the dark anymore, and sometimes not in the daytime either.