To be clear, this is when important information is passed and understood between two people without any need for words.
And he doesn't much like it
In the middle of a ludicrous battle for the fate of the human race, Nia says something that seems a little off. Simon looks at her, she looks back at him...and just like that, he understands completely. In a single glance and wistful smile, she conveys to him that 'I'll die if you win here...but I'm okay with that'. No words exchanged, except for a reminder form her that he came out here to do what he needed to.
For the movie edition this beautiful moment actually got cut out and replaced with something much more hamfisted, which is a damn shame and is one of the reasons I feel conflicted about said movie.
That's just. Water in my eyes.
Vivi, for the uninitiated, was a member of the Straw Hat pirate crew for several arcs. After Luffy defeated Crocodile and thus saved her kingdom, she elected to remain behind and help rebuild. There was a tearful farewell, Vivi broadcasting her goodbyes over a loudspeaker while the Marines surrounded the Straw Hats' ship. And at the end, she asked them a final question: If they met again, would they still consider her a friend?
And of course, the answer was yes. But if they answered that loud enough for her to hear, with the Marines closing in around them, it would cause her no end of trouble. They couldn't declare her to be one of them without setting the government on her tail. And so they would have to say farewell in silence...
Which they did by turning around, raising their left arm, and showing off the black Xes they had marked there earlier to help protect against infiltration by a shapeshifter - those stupid black Xes that the readers had all forgotten about - holding the sign of their friendship on high for her to see. And although not a word was passed back, she understood, and responded in kind.
I know, I know, the quality's shit. It's the only copy of the scene on YouTube with the sound not horribly out of sync.
OK first what you have to understand about Basquash! is that it is a show about basketball played in giant robots. The second thing you have to understand about Basquash! is that there is a team of players of the eponymous sport who are also a wildly successful idol band from the moon (the moon is a giant city. Earth is the slums). The first time we see them play (against the protagonists), the timer for the match is until the end of their hit song Running On, which Rouge sings while playing.
Their semifinal match against the protagonists is, however, cut short when Rouge collapses on the field. There is circumstances here too complicated to bother going into, but basically shortly thereafter, her teammates inform Dan that she's being sent back to the moon for medical treatment, and will probably never come back; if he doesn't go talk to her now, he might never see her again.
Like the dumbass he is, he arrives too late and winds up futilely chasing her limo down the street on foot.
So what does he do? He gets into his giant robot, he picks up his enormous basketball, and starts bouncing it around the city so that the timing of the bounces sounds like the rhythm of the song she sang when they first played each other, so that she hears it as she's flown away. A wordless promise to her that they'll meet and play basketball again.