How to assert my authority without feeling like I'm just being bossy.

Stop worrying about sounding like the B word. Keep it civil - talk to them the same way you would want a supervisor to talk to you about your job duties. Don't address an issue when you're too angry to control your tone. Please and thank you are two of your best tools.

Appropriate delegation and supervision is one of the requirements of our license - you don't need to apologize for it.

You might get called the b word. So what? You aren't at work to make friends. As long as you're being fair and professional within the bounds of your job description it doesn't matter.

Remember that the NAs are working under your license. If something goes wrong it ultimately ends up on you unfortunately. You might get called the b word but it's either that or lose your license. Your there to protect your patients and the NAs need to understand that it's everyone's job and a team effort. I would talk to them calmly and explain just that to them, and if it persists write them up or talk to your manager.

Oh there you are! You probably didn't realize that Jane is on her lunch break on off of the unit right now, we can't have both of you on break at the same time.

Be prepared to give a reasonable task.

It's all about the tone.

B---y: "You need to get your butt out here."

Pushover: "Could you pleeeease come out? I really need sone help!"

Authoritative: "While one of you is on break, both of us do need to be on the floor. Thanks!"