Medical Trainee
Medical Assistants are essentially Staff Assistants with built in access to Medbay. Medbay tends to have so much traffic that it is not hard to walk in to begin with, so this is often not that big of a deal. Nominally, your job involves following around the a Medical Doctor and helping him with triage, or working alongside a Roboticist or Geneticist while they do whatever it is they do. This makes it a great job for a new player - simply ask someone if they could show you how to do their job, and they will often happily do so.
In practice, however, assistants are often skilled players who joined too late to get any other job. Without more productive work, these skilled players quickly get bored and resort to hooliganism, harassing anyone they come across and physically assaulting anyone who doesn't look like they're paying attention. This can lead to a lot of suspicion, so don't take it personally if someone treats you like you're radioactive. More than likely, an assistant knocked him out and stole his shoes earlier in the round.