Hey, relax.dude was desperate to get laid. I've heard much worse lines.
I can see him using the same "most amazing thing wasn't them, but you" thing at a bar trying to pick up chicks when their marriage goes bad, which judging by her baggage wouldn't be long..put it in a sequel!!!

"The most amazing thing to ever happen to me." is the worst line in the movie. I don't recall that in the short story and even if it wasn't it's fine. It's really the choice to use those words that made it a bit campy. Especially since the build up wasn't there. The fact that they were hiding as much of their romantic connection as possible for the reveal suggests this and doesn't help the problem. I would have preferred something less overtly strong considering they had planned to limit their early onscreen connection. Something like "A lot of scientists would say this was the most amazing thing to happen to themand maybe it wasbut I'm also pretty glad to have met you (or gone through it with you)". At that point in the movie (if I remember right) as far as the movie wants the viewer to knowhe's still just a close colleague at best. Something like that would work as a more subtle hint that he might be interested in her. Then comes that shot later where we see his face as the dad.

The line in the movie was pretty much word for word from the short story but didn't really carry over as well to the screen unless you had read the short story

Both lines were cringe worthy.
Schrodinger's cat walks into a bar and doesn't.

I agree. No matter when the line was spoken it was cringe worthy.

Did you even watch the movie?

Yes they got married first correct

Really??? Can you not see that this last scene is at some time after the aliens have left. They're at her (their) place obviously married by now cause she's wearing her wedding band. It's not like they just left the army camp and on their first date.

It came out of nowhere for Ian, who couldn't see the future.
"Let's make a baby" to a woman he barely knew? Who says that?

Funny, I thought both lines were great. The book ends with the same line, it's why it's called Arrival (movie) and Story of Your Life (short story). Like the Heltapod language, it's not linear, there's no beginning and no ending. That final line followed by the panning of the camera and the word ARRIVAL to end the movie was perfection.
If you were paying attention, you'd realize that it did not come out of nowhere, every shot in the movie leads to that last line.