Even that analogy makes it sound more severe as it’s a door that you’ve been asked to stay out of. They used a door that they frequently are required to use but for a purpose other than what they were authorized to do. Eg. You can use this door to do A but you use the door to do B.

Or, car analogies! You are given a car for work and told it can only be used for business purposes, but you use it to drive to the grocery.

Or, something closer to technical which may be familiar to people. You’ve given a laptop for work only but you browse HackerNews on it.

All are against the policies of those that granted you access to the device, but would they constitute unauthorized access?