For the first issue, I would question whether this dog is actually suddenly becoming aggressive. It's probably more like this: The dog is so excited that it wants to take out it's excited energy on something. (This is the most likely cause.) Since biting/chewing is calming to dogs and is fun, he decides to bite something, and that just happens to be this person's partner. In this case, the owner should make sure the dog has calmed down before going for a shower, should make sure the dog has had enough exercise an mental stimulation, and the partner should try to redirect the dog to a toy or chew.
For the second: The dog seems to be scared by the owner putting on the lead, and is therefore defending itself. The owner should make sure they aren't leaning over the dog when attaching the lead, as this can seem threatening. This is one of the most common causes for this issue, especially in small dogs. They should also make sure the collar/harness and leash are comfortable. If the dog is scared of the leash itself, they could try slowly getting the dog used to having the leash around before trying to attach it. They should be sure not to suddenly and quickly approach the dog and clip the lead on. They should make sure the dog sees them coming with the leash, and is prepared for them to clip the lead on. If the leash is on a choke chain, then, regardless of anything else, that choke chain needs to go away, they're dangerous and potentially deadly. If the leash is on some other aversive tool, like a front-clip harness, head halter, or prong collar, or if they use the leash to give corrections or "leash pops", they should stop. The dog is not responding well to that method of training, and is becoming stressed.
This owner may want to consult a vet. A dramatic change in behavior, especially one relating to biting, could be indicative of a medical issue.
For the second: The dog seems to be scared by the owner putting on the lead, and is therefore defending itself. The owner should make sure they aren't leaning over the dog when attaching the lead, as this can seem threatening. This is one of the most common causes for this issue, especially in small dogs. They should also make sure the collar/harness and leash are comfortable. If the dog is scared of the leash itself, they could try slowly getting the dog used to having the leash around before trying to attach it. They should be sure not to suddenly and quickly approach the dog and clip the lead on. They should make sure the dog sees them coming with the leash, and is prepared for them to clip the lead on. If the leash is on a choke chain, then, regardless of anything else, that choke chain needs to go away, they're dangerous and potentially deadly. If the leash is on some other aversive tool, like a front-clip harness, head halter, or prong collar, or if they use the leash to give corrections or "leash pops", they should stop. The dog is not responding well to that method of training, and is becoming stressed.
This owner may want to consult a vet. A dramatic change in behavior, especially one relating to biting, could be indicative of a medical issue.