Regardless of whether a law enforcement officer or agent is in uniformor plain clothes, it is important that they carry themselves professionally at all times. This doesn't mean just keeping clean and tidy. Officers need to be mindful of the fact that they represent more than just the agency they work for; they represent the community and the people they serve as well.
There is no set standard in the United States for what constitutes a reasonable speed in a vehicle. Posted speed limits have come to mean very little, especially on interstates. In Connecticut, a mile over the posted speed limit will net the driver a ticket. In Wyoming, the interstates have virtually no speed limit. So, an acceptable speed all depends on where you are.
The public may be fickle at times; it may seem indifferent to the people serving as officers and agents of law enforcement. But overall, the public is made up of a law-abiding group of citizens who indirectly create the laws to be enforced, and directly finance that enforcement. By virtue of the existence of these two conditions, the general public has the right to expect a certain level of performance from their public servants at all times. Professionalism is the minimum behavior to which the public is entitled.
Since law enforcement officers represent the community they serve, they also need to be representative of that community. This does not mean that predominantly white neighborhoods need to be served by white police officers. It means that the decorum and bearing of the agent needs to be worthy of the people. In criminal courts of law, the prosecutor addresses the court proceedings to The People, The State, or The Government. To truly be a representative of the people, that prosecutor needs to be representative of the people as well.