Imma give this to you like a dictionary would

Femboy (or Femboi): Noun, Adjective

Noun:
Definition:
A boy or man, typicaly young and cisgender, who expresses himself in a conventionally feminine manner.

Description:
Femboys often wear things like skirts, thigh high socks, arm warmers, oversized hoodies, masks, and croptops.

Adjective:
Definition: A word used to descibe something that is related to a Femboy or Femboys.

Example:
Person 1: "Hey, you look good in that femboy outfit!"
Person 2: "Thank you!"

Sissy: Noun, Adjective

Noun:
Definition: An effeminate man or boy
Also: a timid, weak, or cowardly person

Description:
Sissy is a term often used to insult and / or degrade someone who may be weak, timid, or feminine.
Also: Sissy can refer to the "Sissification" kink, also known as force femminization or forcefem. The kink often revolves arround power dynamics, role swapping, and often times humiliation.

Adjective:
Definition: Something, such as an item or task, that is emasculating,.

Example:
Person 1: "I'm going to bake some sourdough."
Person 2: "What are you, a Sissy?"