Starbucks Sued By Customer Who Says He Got Served Cleaning Solution

Starbucks usually gives its customers a caffeine jolt, but one guy says he perked up for entirely different reasons ... claiming the coffee giant poisoned him with a cleaning solution.

A man named Matthew Mitchell is suing the green mermaid company for what he claims was a reckless display from management when he allegedly downed a black coffee ... which turned out to be blue, and NOT any type of java in the slightest.

In the docs, obtained by TMZ, Mitchell claims he ordered a simple coffee beverage from a Connecticut location last August ... which was promptly served, and which he threw down the hatch without even thinking twice.

Almost immediately, however, Mitchell says when he drank what turned out to be a witch's brew, he immediately felt a burning in his throat and chest. He looked down in his cup and saw a blue liquid ... turns out it was a chemical substance -- causing his stomach to turn upside down within seconds. Mitchell alleges the staff told him a new employee had screwed the pooch ... not realizing they were brewing coffee in a machine that had just gotten a Urnex treatment.

If you're unfamiliar ... Urnex has a product called Urn and Brewer Cleaner, which Starbucks uses to purify its brewing machines. Problem is, according to Mitchell, Starbs has a crappy system to alert employees when the cleaning is going on -- an upside-down cup and nothing more, he says -- leading novice workers to serve customers like him tainted cups of Joe.

Mitchell says this system is BS -- insisting a more thorough process should've been in play to prevent the nightmare -- and hits the point home, claiming Starbucks was cutting corners here ... which caused great pain and suffering on his part. As a matter of fact, Mitchell claims at least 2 other alleged poison victims sued Starbucks for the exact same thing in the past.

While he was treated for the alleged poisoning, Mitchell says he continues to deal with the fallout -- including what he says is heightened anxiety and fear about the long-term effects of the Urnex ... not to mention medical bills, etc.

For all this trouble, Mitchell says Starbucks is completely responsible ... and he's asking a judge to award him a boatload of cash in damages, laid out in explicit terms by his dynamo attorney, Joe Tacopina.

We reached out to Starbucks, who said, "Our baristas take great care in crafting beverages and providing a safe experience for our customers. We take this obligation seriously and are reviewing Mr. Mitchell's claims."