I have a very very small penis but I use that phrase all the time. Mostly when I get aggressively passed by someone in a lifted pickup that cost more than my kidneys would fetch on the black market who has modded the tail pipes to be as loud as possible (this is a common occurrence where I live).

Tiny penis energy isn't about the size of their literal penis. It's about them being insecure about something (quite possibly the size of their literal penis, among other things) and acting like a fucking tool to compensate. It's the shithead behavior that stems from being like that and having no idea how to handle it in a healthy or not-obnoxious way.