"Rizzmas" is a combination of "Rizz" and "Christmas". Assumingly, "Rizzmas" is when someone, perhaps a "Rizzler", "pulling" multiple partners near or around christmas time.
(This example is a work of fiction. Any references to real people, places etc is purely coincidental.)
Dave: "Yo man," he enthusiastically yapped as he slapped John's shoulder, "it's almost rizzmas, man!"
John: Unamused, John snarkily retorts, "You motherfucker, you didn't pull nobody all year! Go ahead and fucking try 'rizzmas' this year and watch yo ass get thundercunted across campus."
Used near the beginning of online streaming, "chat" is commonly used to refer to a group of people in an online stream or chatroom.
"Chat, I just hit a nasty clip."
Recently heard in a viral song, whose lyrics are "sticking out your gyat for the Rizzler, you're so skibidi, you're so fanum tax", Rizzler is derived from "Rizz", a shortening of "charisma" that takes the "rizz" sound in the "ris" of "charisma". "Rizz" more specifically is geared towards "pulling", the act of gaining female/male/other partners in excess. Therefore Rizzler, or more appropriately a Rizzler, is someone who has an abundance of "rizz", and often "pulls".
(This example is a work of fiction. Any references to people, places, etc is purely accidental.)
Dave: "Yoooo checkout Jake, he has like eight chicks around him!"
Jake: "I'M A RIZZLER, MAN!"