About
This is a commonly used phrase in conversations revolving around girls when one is simping hard for the girl, mostly used in the anime community.

Origin
On November 6th, 2020, Japanese channel Fumiin posted a video of a man chasing behind a car while loudly shouting about sex. Many things made the video funny beyond the screaming, such as how the man was keeping up with the car, how he was actually on a bicycle but many people thought he was frantically sprinting, which made the video even funnier. This was also posted on instagram and it blew up there.

Spread
On March 25, 2021, a variation video of the original was posted on YouTube with translations for the words the man says, along with a very well-known and iconic soundtrack from the anime My Hero Academia which made it very popular overseas, and especially within the anime community because of that and the fact that the original video is in Japanese
Eventually, the shouting sound was made into a word that was then fused with the known variation of the word sex, Seggs, along with capitalization of all letters to imply the shouting part from the video, to form this phrase.