Cut hardboiled egg into two pieces, lengthwise, so that one half is slightly larger than the other. Remove egg yolk from both halves and set aside. On the larger half, cut out a little extra space on the inside to make your egg white "carriage" slightly more spacious. Cut the smaller half of the egg in half crosswise. Skewer a carrot slice onto the end of a toothpick, then do the same with a pickle slice so that the pickle slice is on the outside edge of the carrot. Stick the other end of the toothpick through the "carriage" section of the egg where you want one set of wheels to be. Once through, secure on the other end with another carrot slice, followed by another pickle slice. Repeat this step to create one more set of wheels at the other end of your carriage. With the egg yolks you set aside earlier, make a deviled egg filling mixing the egg yolks with the mayonnaise, mustard, vinegar, onion, hot sauce and salt and pepper. Scoop this filling into your carriage. With the top piece you cut from the smaller egg half earlier, create a dome on one end of your carriage by gently pressing the egg into the deviled egg filling. The ends of this piece should rest inside the carriage structure and you may have to squeeze the ends together slightly to accomplish this. Cut a slice crosswise from a sausage--it should be about 1/4" thick and then trim a bit from the outside to create a slightly smaller circle that fits more easily inside the dome of the carriage. Stick two chocolate sprinkles side-by side into the sausage so that they look like eyes. Cut a curved sliver from a black olive and press onto the sausage so that it looks like the baby's mouth. Press the baby's head into the deviled egg filling just inside the dome section of the carriage. For the body, cut another slice from the sausage and trim off two sides so that you have a more rectangular shape. Trim off a little but from one of the remaining curved edges so that only one edge and you still have a slightly oblong shape. Press the body into the deviled egg filling with the curved edge facing away from the baby's head. Use some of the sausage pieces you cut off earlier to create arms and legs--these should be roughly rectangle-shaped. Press the arms and legs into the deviled egg mixture.