“Caesar salad” (a salad of romaine lettuce and croutons) has nothing to do with Julius Caesar, the Roman emperor who was assassinated on March 15th (“the Ides of March”). The salad was named after Italian-American restaurateur Caesar Cardini (1896-1956).
 
“Somewhere out there, there is a bottle of Cesar salad dressing with an expiration date of March 15th.” is a jocular saying that was posted on Reddit—Shower Thoughts on March 16, 2014. “This Caesar Dressing Expires On the Ides of March: was posted on Reddit—Mildly Interesting on March 13, 2016
   
“Somewhere there’s a bottle of Caesar salad dressing with an expiration date of March 15” was posted on Reddit—Shower Thoughts on January 7, 2018.
   
       
Wikipedia: Julius Caesar 
Gaius Julius Caesar (Classical Latin: [ˈɡaː.i.ʊs ˈjuː.li.ʊs ˈkae̯.sar]; 13 July 100 BC – 15 March 44 BC), known as Julius Caesar, was a Roman politician, general, and notable author of Latin prose. He played a critical role in the events that led to the demise of the Roman Republic and the rise of the Roman Empire.
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Plutarch also reports that Caesar said nothing, pulling his toga over his head when he saw Brutus among the conspirators. The version best known in the English-speaking world is the Latin phrase “Et tu, Brute?” (“And you, Brutus?”, commonly rendered as “You too, Brutus?”); this derives from Shakespeare’s Julius Caesar, where it actually forms the first half of a macaronic line: “Et tu, Brute? Then fall, Caesar.” It has no basis in historical fact and Shakespeare’s use of Latin here is not from any assertion that Caesar would have been using the language, rather than the Greek reported by Suetonius, but because the phrase was already popular when the play was written, it appears in Richard Edes’s Latin play Caesar Interfectus of 1582 and The True Tragedie of Richarde Duke of Yorke & etc. of 1595, Shakespeare’s source work for other plays.
 
Wikipedia: Caesar salad
A Caesar salad is a salad of romaine lettuce and croutons dressed with parmesan cheese, lemon juice, olive oil, egg, Worcestershire sauce, garlic, and black pepper. It is traditionally prepared tableside.
     
Reddit—Shower Thoughts
Somewhere out there, there is a bottle of Cesar salad dressing with an expiration date of March 15th.
submitted March 16, 2014 by Zodikosis
   
Twitter
Ed‏
@_EdTheGreat
Somewhere out there, there is a bottle of Cesar salad dressing with an expiration date of March 15th
5:39 PM - 16 Mar 2014
 
Twitter
Presley‏
@PresleyFrench
Somewhere out there, there is a bottle of Caesar salad dressing with an expiration date of March 15
9:26 PM - 16 Mar 2014
 
Twitter
Madeline Alaska‏
@madmadv3
Somewhere out there there is a bottle of Caesar salad dressing with a March 15 expiration date
9:39 PM - 16 Mar 2014
 
Twitter
Rohan‏
@therohanization
Somewhere out there is a bottle of Caesar salad dressing with an expiration date of March 15th…
11:49 PM - 16 Mar 2014
 
Twitter
Matt Kimbro‏
@MattKimbro
Somewhere out there, there’s a bottle of Caesar Salad dressing with an expiration date of March 15.
2:42 AM - 17 Mar 2014
   
Reddit—Mildly Interesting
This Caesar Dressing Expires On the Ides of March (imgur.com)
submitted March 13, 2016 by swagfleekneat
COMMENTS
Smgth
Fun fact: Caesar dressing is named for Caesar Cardini, an Italian immigrant who operated restaurants in Mexico and the United States…probably.
 
Reddit—Shower Thoughts
Somewhere there’s a bottle of Caesar salad dressing with an expiration date of March 15.
submitted January 7, 2018 by Stranga_Danga
 
Twitter
Joseph Palmer‏
@Joseph_Palmer
(From Reddit) Somewhere out there there is a bottle of Caesar salad dressing with an expiration date of March 15
11:11 AM - 7 Jan 2018