Question: Why would liquid half-and-half creamer curdle when poured into hot coffee? This happens to me sometimes, and I'm not sure why. Could it have something to do with either the coffee being too hot or the creamer being too cold?

Answer: 
I watched an episode of Blue Bloods where Mr. Selleck explained to his grandkids that the secret to not having your cream curdle in your (Irish) coffee was to hold your spoon upside down over your coffee and pour the cream over the back of the spoon. I tried it and have never had curdled cream in my coffee since. Don't know why it works I just know that it does. I'm guessing it might have something to do with increasing the dispersion of the cream.
I had this happen to me in the most bizarre circumstance. I buy green coffee beans and roast them myself at home. I have decaf and regular that I roasted separately, then grind them together to make half decaf and then brew my coffee via pour over ( no machines). I did this and then used soy creamer (brand new, not old). Didn't curdle. Then, I brewed a cup with just the regular beans (no decaf). Same way, same day, everything the same other than it was full caff. Added the same soy creamer and it curdled. I repeated this exactly the next day and it did it again!! My guess is it has to do with the acidity of the coffee beans.