So this guy who played classic guitar was showing me the most intense thing i've ever seen. Impressive as hell. He also said it was really hard. It was a bunch of arpeggios, and he said it went "i-m-" or something, like the strings started out as 6, 4, 5, etc...does anyone know what that is called?
I think he might have been referring to p-i-m-a. In fingerpicking your fingers can be labelled p-i-m-a to show which fingers to use.

P - Thumb
I - Index
M - Middle
A - Ring

The pinky finger is generally not used and thus doesnt get an initial to represent it. The initials are derived from the spanish words for those digits. Pulgar, Indice, Medio and Anular.
Yeah, he was using that to describe a way he was playing those arpeggios. He used the pinky in it though.

Thanks for the answer

Does anyone know the actual thing he was referring to?
I got it - it was the fingering style used in Heitor Villa-Lobos's Etude No. 1