I happened to find a very good Cantonese learning video by MissYau’s Asian-SuperAsian Channel.
We can learn these “Scary” Cantonese expressions:

1. 你玩嘢啊?（lei wan yeh ah?)  Are you kidding (me)? Playing games?
2. 你买定棺材啊你！（lei mai ding goon choi ah lei.)  Put a down payment on your coffin. Or get your coffin ready. It’s a threat or curse.  Are you scared yet? Watch this fun video.
3. 唔好煩啊你 （Mm – mo – fan – ah – lei. ) Don’t be a nuisance. Or “Stop bothering me.”

Please note that she does not use Jyutping.  For Jyutping, it is like this: 1.

简体	你	玩	嘢	啊
繁體	你	玩	嘢	啊
粤拼	nei5	waan4	je5	aa4
Yale	nei5	waan4	ye5	aa4

2.

简体	你	买	定	棺	材	啊	你
繁體	你	買	定	棺	材	啊	你
粤拼	nei5	maai5	ding6	gun1	coi4	aa1	nei5
Yale	nei5	maai5	ding6	gun1	choi4	aa1	nei5

3.

简体	唔	好	烦	啊	你
繁體	唔	好	煩	啊	你
粤拼	m4	hou2	faan4	aa1	nei5
Yale	m4	hou2	faan4	aa1	nei5

More and more people are using "lei" instead of "nei" for 你(you), even for people older than me. Is it SCARY Cantonese or not, but it's basic Cantonese, or colloquial Cantonese. It is Cantonese youtube, or Youtube Cantonese lesson. Way to go MissYau!