Sometimes adrenaline does funny things to your body. There have been a few times in intense situations where I literally could not say more that one syllable. Almost as if in a dream state I tried to say the words I was thinking in my head, but could only say “no”. One thing that experience has taught me is that even short sentences may be too much.
I adamantly believe in having a command to signal to personal space invaders that you do not want any.
My one word command actually came to me while doing push ups. A while back I had a sweet, but very needy dog that always wanted to be a part of what I was doing and would try to get pets while I was working out. The “no” command didn’t work, but “space” did.
It’s partially what you say and partially how you say it. I envision throwing a bean bag when I vocalize that word.
This may not be your word, but I advise you to come up with something that you can say that quickly conveys that you do not want someone in your personal space and practice saying it.
Practice somewhere you can be loud. Practice saying it with force. Imagine saying it during an unsolicited hug attempt. Practice saying it strongly, but in a speaking tone, imagining that a drunk family member or friend is hovering over you. Practice shouting it full force, in an attempted assault.
It doesn’t matter if you sound funny in your head or if it makes you a little uncomfortable. It’s better to experience that now than in an intense situation.