Ashton Kutcher & Mila Kunis Run-In with Leo DiCaprio at Fancy Airport

You might run into someone you know at the supermarket and stop for a chat -- but when you're as rich and famous as this group here ... you do it on a fancy-schmancy runway.

Check out these photos of Ashton Kutcher and Mila Kunis casually bumping into Leonardo DiCaprio at the Van Nuys Airport Friday as they each seemed to be coming from and going on respective trips. This is where A-listers escape L.A., BTW -- forget LAX.

Word is, MK and AK were coming back from a getaway, and Leo was heading out. But, along the way, they ran into one another and exchanged pleasantries -- specifically, Mila and Leo.

As you can see, LDC was sitting down and smoking a cigarette, when Mila suddenly comes up to him ready to fist bump -- which Leo was happy to reciprocate. Looks like Ashton might've been busy getting their stuff ... no sign here of him and L-dog together.

Later, Mila was seen with her husband loading up bags into a car ... and Leo was left with his ciggie alone. Now, as for what they might've talked about -- there's lots of possibilities.

Of course, one of the topics that very well could've been brought up is Ukraine -- and each party's involvement with contributing financial aid to the country as they fight Russia. Ashton and Mila recently got a shout-out from Zelensky after they raised north of $35M.

Leo, for his part, is also said to have donated some dough to orgs that support Ukraine -- but he was falsely reported as having donated $10 mil of his own money ... a piece of fake news that got circulated online, which was debunked by the Associated Press.