If your family would not be supportive, I wouldn’t go for a big announcement at a Christmas dinner or anything like that, seeing as you are just discerning - I’d save any big announcements for when you can announce that you’re entering the seminary, if you do. If they will be supportive, then announcing it might be the right thing to do.
It wouldn’t have been for me, because my siblings are not particularly supportive of the idea (they’re not against it though).
I don’t know how old you are or what you are doing at the moment, but I’m 22 and studying at universtity and have been discerning a vocation to the priesthood for about 4 and a half years and here’s what I did:
I’ve never ‘announced’ it, I told my mother (who is very supportive) first in conversation, then I told my siblings as the opportunities presented themselves. And now when I talk to people about what I’m doing - studying Classical Languages - and get the question that goes something like ‘What are you going to do when you’re finished?’ I just say (depending on who’s asking) ‘I’m considering the priesthood’ or ‘I’m not really sure’ (both of which are true).
So while you’re discerning, you can just tell people ‘I’m thinking about becoming a priest’ or something like that if it seems appropriate or helpful to tell a particular person. (You may be surprised by how many people say they will pray for you when you do tell them.)
As for seeming cool - what is there in the whole world thats more cool than the Priesthood?

But seriously, if Christ is saying to you 'Come, follow me", you don’t stop to look around at what other people think.