“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” A wildebeest version is:
     
“A wildebeest walks into a bar and the bartender says, ‘Well, this is gnu.’”
   
The joke was posted on Reddit—Dadjokes on June 3, 2021, and again on Reddit—Dadjokes on June 3, 2022.
     
There are other versions. “[3 wildebeest walk into a bar, wearing leather jackets and smoking] ‘Shirley, call the cops. These guys look like bad gnus’” was posted on Twitter by Sean Leahy on September 15, 2015. “A wildebeest walks into a bar, sits down. Another wildebeest says to the bartender, ‘Who’s the gnu guy?’” was posted on Twitter by ß¡|| Evenson on October 22, 2016.
 
   
Wikipedia: Wildebeest
Wildebeest (/ˈwɪldɪbiːst/ WIL-dib-eest, /ˈvɪl-/ VIL-, /-dəb-/), also called gnu (/njuː/ NEW or /nuː/ NOO), are antelopes of the genus Connochaetes and native to Eastern and Southern Africa. They belong to the family Bovidae, which includes true antelopes, cattle, goats, sheep, and other even-toed horned ungulates. There are two species of wildebeest: the black wildebeest or white-tailed gnu (C. gnou), and the blue wildebeest or brindled gnu (C. taurinus).
   
Twitter   
Sean Leahy
@thepunningman
[3 wildebeest walk into a bar, wearing leather jackets and smoking]
“Shirley, call the cops. These guys look like bad gnus”
6:07 AM · Sep 15, 2015·TweetDeck
   
Twitter
ß¡|| Evenson
@BillEvenson
A wildebeest walks into a bar, sits down. Another wildebeest says to the bartender, “Who’s the gnu guy?”
2:55 PM · Oct 22, 2016·Twitter for iPhone
 
Reddit—Dadjokes
Posted by u/Firegoat1 June 3, 2021
The wildebeast
A wildebeest walks into a bar and the bartender says, “Well, this is gnu.”
   
Twitter
Jesse Ras
@JesseRas
Here’s a #DadJoke for the @LouisvilleZoo !
A wildebeest walks into a bar and the bartender says, “Well, this is gnu.”
#DadJokeFriday #DadJokes
@mix1069lou
9:24 AM · Jun 4, 2021·Twitter Web App
   
Twitter
gimme your waffle
@tsjwaffle
Replying to @melissamonetxxx and @TheCaucusHost
A wildebeest walks into a bar and the bartender says, “Well, this is gnu.”
8:53 PM · Sep 13, 2021·Twitter for iPad
   
Twitter
Devin Dingler 🇺🇦
@DevinDingler
A wildebeest walks into a bar and the bartender says, “Sorry buddy, no can do.” The angry gnu points out that several of his ilk are standing at the bar. “That’s the thing,” he says, “they’re all here for some big NY Times event and that’s all the gnus that fits.”
#tweet100
9:25 PM · Oct 15, 2021·Twitter for iPhone
 
Reddit—Dadjokes
Posted by u/Firegoat1 June 3, 2022
A wildebeest walks into a bar
The bartender says, “Well, this is gnu.”