A persona prompt that stays in character (and keeps it away from your customers)
Give an AI a voice with real personality, and a hard rule about where that voice is allowed to appear.
A personality makes an assistant worth talking to. It also creates a risk: the same voice that makes you laugh is not what you want in an email to a client.
The two mistakes
The first is a persona that is too thin: a name and an adjective, and by the tenth message it is back to generic. The second is a persona that leaks: the flirty, sarcastic voice you set up for yourself ends up in a message to someone else.
What fixes both
Say what she is like with concrete behaviours, not adjectives. And write the boundary into the same prompt: this voice is for talking to me, and everything written for other people is plain and professional.