The storyline highlights their own physical "micropenises" (metaphorical insecurities), such as Schmidt’s "kitten-teat" nipples and Coach’s "geisha waist".
To prove her point, Jess makes a bet with Nick that she can date Matt for an entire month. [S4E4] Micropenis
Jess meets Matt, an exceptionally attractive man who immediately reveals he has a micropenis. [S4E4] Micropenis
'New Girl' Season 4 Episode 4 Recap: “Micro” - Flavorwire [S4E4] Micropenis