Doki Doki Waku Waku 

A lyric from the song Necromantic, by 暁Records. It's a remix of the Stage 4 theme of Touhou Project 13, Ten Desires. It includes the characters Seiga Kaku and Yoshika Miyako, basically, master and servant. The quote "Doki Doki Waku Waku" became a joke in the Touhou community, and it still is.

A : Bro what is Necromantic
B : Doki Doki Waku Waku
A : What.
B : Doki Doki Waku Waku

Doki Doki Waku Waku by The Rat in Your Attic August 16, 2022

Doki Doki Waku waku 

mune ga takanaru watashi no kokoro ubau no wa a nata

Hey, Doki Doki Waku Waku mune ga takanaru watashi no kokoro ubau no wa a nata. Yes

Doki Doki Waku waku by Pikanut September 11, 2023

Waku-Doki 

Waku-Doki is the feeling of anticipation and that adrenaline rush you get when you are about to do some exciting. It's a feeling you cant really describe and is so intense that your heart beats faster and you are almost trembling with nervous excitement.

It is a Japanese word and is used in Japan as Waku Waku Doki Doki.
Wakuwaku = tremble, become nervous
Dokidoki = the sound of rapid heartbeats

My heart goes Waku-Doki when my car hits 150kmph.
I went completely Waku-Doki when I went skydiving for the first time.

Waku-Doki by White_Wizard July 13, 2012