“Open mic” (or “open mike”) means that an entertainment venue (such as a nightclub or a comedy club) has an “open microphone” where people can sign up to perform. It doesn’t mean “opening a person named Mike,” but there have been several puns.
 
“Open mike night at the morgue” was posted on Twitter on December 3, 2010. “I’m sure the morgue has open-mike nights” was posted on Twitter on February 7, 2012. “‘It’s open mic night at the morgue. They’re gonna autopsy a guy named mike’ LOL disney channel cracks me up” was posted on Twitter on April 5, 2015.
 
“I don’t normally go out, but Open Mike Night sounded fun. Then we got to the morgue” was posted on Reddit—Jokes on November 10, 2017.
   
         
Wikipedia: Open mic
An open mic or open mike (derived from the expression “open microphone”) is a live show at a coffeehouse, nightclub, comedy club or pub where audience members who are amateur performers or professionals who want to try out new material or plug an upcoming show are given the opportunity to perform onstage. Typically, as the name suggests, the performer is provided with a microphone which is plugged into a PA system, to make the individual’s performance loud enough for the audience to hear. Often the performers sign up in advance for a time slot with the host or master of ceremonies, typically an experienced performer or the venue manager or owner. The master of ceremonies may screen potential candidates for suitability for the venue and give individuals a time to perform in the show. These events are focused on performance arts like poetry and spoken word, music (often singer-songwriters who accompany themselves on guitar), and comedy. Less commonly, small groups, such as a small rock band duo/trio or a comedy duo may appear. Group performances are uncommon, because of the space and the logistics of loading in and soundchecking such a group.
 
Merriam-Webster Dictionary
open mic
noun
:an event in which amateurs may perform (as at a comedy club) usually without auditioning first
First Known Use: 1978
   
Twitter
Helena Medeiros‏
@MedeirosHelena
Acabaram as apresentações oficiais
E de repente virou “open mike night at the morgue”... JESUS!!!
#takingthewrongturntothedouche
Translate from Portuguese
7:47 AM - 3 Dec 2010
 
Twitter
T. P. Gildersleeve‏
@LoveYourOutfit
I’m sure the morgue has open-mike nights.
2:39 PM - 7 Feb 2012
 
Twitter
Steve “Get rid of the Nazis already!” Mieczkowski‏
@IGotsSmarts
Pathology students get their start at “Open Mike” nights at the morgue.
4:27 AM - 16 Apr 2012
 
Twitter
Mari, Anishinaabe (Ojibwe) Writer オタク‏
@CyborgN8VMari
Replying to @LoftEintentions
@LoftEintentions Funny, usually my jokes only kill at the morgue’s open mic night. Cool crowd.
7:58 PM - 30 May 2014
 
Twitter
Julie ✨‏
@jewelsshanny312
“It’s open mic night at the morgue. They’re gonna autopsy a guy named mike” LOL disney channel cracks me up
1:05 PM - 5 Apr 2015
 
Twitter
Im All Write 🤔‏
@imallwritecom
“Welcome to open mike night!”
- ongoing joke at the morgue
7:45 AM - 27 Jul 2017
 
Reddit—Jokes
I don’t normally go out, but Open Mike Night sounded fun.
submitted November 10, 2017 by MetaphoricMenagerie
Then we got to the morgue.
COMMENTS
sutree1
/Mike dropped
 
Zaphod_Spinach
You tapped on the Mike and discovered it was dead.