Like Gabriel says, that doesn't mean I'm not passionate, but others may interpret it as such, or think that I don't care at all about anything.
When something happens and I feel like there's a risk of someone misinterpreting my lack of visible reaction as something it isn't... I give a visible reaction.
That is, if something legitimately good and exciting happens, and I'm the only one in the room not celebrating, I'll force a smile/laugh/shout if there's someone present who doesn't know me well enough to understand my stoicism.
I don't feel like a fraud or phony for doing this; doing it is like accommodating a guest. If I raise my voice when talking to someone who has hearing loss, I'm not faker, even though I don't normally talk that way. If I use simple English to talk to someone who primarily speaks Spanish, I'm not being duplicitous.
It's not a disavowal of my personality or "wiring" to do this; it's a recognition that not everyone is so familiar with me to understand my particular emotional set point.