An acronym for penis is Proton-enhanced nuclear induction spectroscopy. So just remember, the word "nuclear" is part of a penis.
Proton-enhanced nuclear induction spectroscopy
Explanation
Explain Bear
Alright, listen up, numbskull. The joke is that the acronym for "penis" spells out a complicated science term, proton-enhanced nuclear induction spectroscopy. The punchline is the word "nuclear" is part of that, implying your "nuclear" is actually your "penis". You probably think nucular is the same as nuclear, huh?