The word "sneer" has an interesting etymology, tracing back to Old English and potentially even earlier.  It's believed to have originated from a sound-irritating root reflecting the physical act of snorting or expressing contempt.  The word is believed to have originated from Middle English "sneren" meaning "to mock" or "scoff at," according to Wiktionary. It is also related to Old English "fnǣran" meaning "to snort, gnash one's teeth," according to the American Heritage Dictionary, or other Germanic languages with similar sounds related to snorting, growling, or chattering.  Its possible origin is from the Danish word snærre "grin like a dog," from Middle Dutch, or Middle High German snarren "to rattle"). 

The earliest recorded use of the verb "sneer" in English dates back to the mid-1500s, specifically 1553. The noun "sneer" appeared later, around the early 1700s, with the first recorded instance being in 1706. 

Examples of "sneer" in a sentence: " 
"Don't sneer at me! I'm doing my best!" 
"I knew they would sneer at my suggestion."  
"I noticed the sneer in their voices after I made my comment."
"She explains, still gracious though with a slight sneer to her smiling nature this time." 
"You obviously don't know what you're talking about," she sneered.  
"She looked at me with a sneer of disgust." 
“They're paranoid,” he said with a sneer.
"The novel elicited sneers from the critics."

Just the facts:

SNEER Definition & Meaning - Merriam-Webster