A Cambodian expression used when a guy talks in a neutral tone while sounding like he's showing off. Either he's joking by blowing it out of proportion or either he's serious and not aware he's sounding like he's showing off. The more the guy shows off, the more 's' you add at the end. Its origins are obscure but it's commonly used by Cambodians from Montreal.
Guy : I went clubbing yesterday
You : How was it?
Guy : Not bad, I hooked up with 10 chicks
You : ESSSSSSSSSSSSSSSSSS!!!
Guy : I bought a Prada shirt yesterday
You : ESSSSSSSSSSSSSSSSS!!!