Is it bad that I don't really care about a friend's engagement?
I'm not sure. Why don't you care about their engagement?
I'm not really an emotional person.
I get not being super emotional about others events. You should at least try to be happy and congratulate them, though.
That's a good point. I'll be sure to congratulate them.
Congratulating them is a good idea because even if you don't feel very strongly about it, they'll be glad to know that you're happy for them during this big time in their lives.