Used to call someone salty. Which is being upset or pissed about something.
Instead of calling someone "salty" Nacl (pronounced nah-cal) is used because NaCl is a common salt.
NaCl-y is Salty. (Salty meaning bitter and negative when talking about a person.) Since according to the periodic table, "Na" is Sodium, and "Cl" is Chlorine, and Sodium and Chlorine is the formula for salt.
Saleshia is so fucking NaCl-y today! She's probably on her period.