The term is derived from the member Alex a.k.a. CurlyWurly on TeenHut forums, who made a thread regarding his yet-to-be shoutout video, that was never uploaded or posted, even though he repeatedly assured other members that it would be uploaded and posted "tomorrow".
2: Don't worry, I will. I'm not going to pull an Alex.
1: Did you hear about Bob?
2: Yeah, apparently he pulled an Alex.