The idea that the original yellow-striped black scheme for the EMD F diesel units could have been called "cutworms" arose in the V-scale forum thread "Constructing St. James, Missouri - Trainz: A New Era" https://www.frisco.org/shipit/index...ing-st-james-missouri-trainz-a-new-era.14985/ . Further discussion about this risked hijacking that thread, so I want to put in another $0.02 here on the subject building on Geep07's comment "What he probably meant was the stripe had a round end and separated by the porthole's resembled a "cutworm" to him." An A-B-B-A set might certainly create this impression, especially if, at heart, the viewer was an avid steam fan. Compare this photo of an ABBA set https://www.frisco.org/shipit/index.php?threads/f7a-slsf-5022.3028/ with a photo of the critter itself from the Colorado State University website https://agsci.colostate.edu/agbio/ipm-pests/army-cutworm/. Notice the color photo on the lower left labeled "5513178."
The term could be one of disappointment and derision for a steam fan hoping to see a 4500, 4400 or 4300 pulling a freight instead of a matched set of 5000s and 5100s.