You want to hear another funny part name? This triangular piece is called a mucket. The CAD guys who design these type of window seal parts get paid big $, because of how much is going on with numerous parts in a small area. They have to figure out how the various surfaces intersect each other, and be able to design something that can be tooled.
Notice how mine was cracking on my 13 R/T? I had it replaced three times on both sides, there were even brand new cars on the lot with this condition. Must've been a bad lot of muckets being produced.