When a single girl blocks the chance of her friend from meeting a guy, not to help her, but out of jealousy
"I was hitting on this girl and we got along really well but then her friend came in and cooch blocked her."
Similar to Cock Block, but a Vagina Block. When a female blocks other female from hooking up with a male cause found out that other female is interested in him. Instead, said female hooks up with male instead of helping out other female.
Jane was interested in John, but Jessica ended up cooch blocking Jane by hooking up with John cause Jessica saw that Jane was interested in him.
Jessica wants John cause Jane wants him. So, Jessica cooch blocks Jane for Johns attention.