@Shelara_Purplematch There’s not really a reason why they named their channel that, but the closest explanation I could find was in their video titled “they don’t want you to see this video...” [https://m.youtube.com/watch?v=m2_qDIDpCH0].
At 4:23 minutes into the video, Josh asks Jordan why they named their channel Blimey Cow, to which they respond that it was something their neighbors said when they were younger and it was one of those “random insults we would say to each other.”