Turtleflexing
The act of flexing one's muscles so hard that their head appears to retract inside of their body.
"Look at that bodybuilder showing off across the gym; you can barely see his face past all that muscle!"
"Yeah, it's a bit much. He spends half his time here turtleflexing in the mirror."
"Yeah, it's a bit much. He spends half his time here turtleflexing in the mirror."