Commonly used by black people in jail.

At the end of smoking marijuana through a glass pipe, one might suck through the ash of the smoked marijuana where a whole forms showing the bottom of the bowl. This hole is known as "his ass"

Fingers in his ass is a meme mainly quoted/said by Danganronpa fans on a site called tumblr or Danganronpa fans in general.
The sentence is usually associated with the pairing sansmaeda. There is also a thing called fingers in his all sunday. On Sundays people gather to appreciate the song fingers in ass and sansmaeda. On December 16th 2018, the day before tumblr's adult content ban fans of sansmaeda and fingers in his ass sunday celebrated what was called the "final" fingers in his ass sunday.

Origins:
On july 17th, 2017 user named skeletortilla uploaded a video on tumblr that had Nagito Komaeda from Danganronpa 2 and Sans from Undertale dancing together to a song called "ASSHOLE (Fingerfückung)" made by BotanicSage on youtube.

Experiencing a difficult time, usually financially

Employing the use of an online encyclopedia to gather information, usually about a peson.

Basically a synonym to "Beat him/her up". It's like cheering someone on when they're roasting another person.

shoot him dead

This extends the toys of the child to the toys of the adult. The cap gun kids shoot each other with is non-lethal. Guns that gangsters kill each other with are hardly toys.