random
weird, out of nowhere, unexpected/odd (broader than literal 'by chance')
Origin
'Random' is borrowed from English 'random' ('by chance'). In German youth slang it is used as an indeclinable meaning 'just like that, for no particular reason and rather by chance' - often extended to 'weird, unexpected, odd/out of nowhere'. The word spread via the internet and social media and is now a firm part of colloquial German.
Building blocks
Words in this expression
Examples
Voll random, dass wir uns .
So random that we'd run into each other here of all places.