Men in Black/Heartwarming

"K: Congratulations Reg, it's a... squid."
 * The alien birth scene, in its own sort of way.

""Your was a hero.""
 * The animated series has a Christmas Special in which Agent K receives the first edition of Charles Dickens' A Christmas Carol. He cracks a smile, and looks like he's about to tear up for the first time in ages.
 * In the third movie, the Colonel's "He showed me how important you two are" becomes heartwarming once you learn that  Also, since Griffin likely showed him

"Seeing K singing The Empire State of Mind happily, which shows that that old curmedgeon finally has a genuine happy moment in his life."
 * The last scene in Part 3 with K and J at the Dinner, where K tell J it's been a privilege working with him.