Having the last word

One of the habits that I find most annoying in people is the need to have the last word.

Sometimes, rarely, it is charming. You are not going to tell my mom "I love you" and get out the door before she tells you the same.

I found a simple, clean way to stop carrying this baggage. I say "Amen".

"The grace of our Lord Jesus Christ be with you all. Amen." Revelations 22:21, KJV 

According to the King James Translation, "Amen" IS the last word of the New Testament. 

If-some-how-ever, you are in a less friendly mood, you can go with the last word of the Old Testament Malachi 4:6

“And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.”

in which case "Curses" might be appropriate.

If you are not of the religious persuasion you can pull out your dictionary:

Zyzzyva: The last word in the Oxford English Dictionary. Zyzzyva, a genus of South African weevils found on or near palm trees

Frankly, I will probably stick with "Amen". I can remember that word.

The other party can say whatever they want after that but is a moot point. You already delivered the Last Word.