Irule to block Requests with specific word

This isn't tested, but may be a useful starting point for you. You can use HTTP::collect to collect payload data and find what you're looking for in HTTP_REQUEST_DATA.

Putting restricted words in a datagroup means you don't have to change the iRule everytime you add a new word.

 DATAGROUP
ltm data-group internal restricted_dg {
    records {
        restricted_word {}
    }
    type string
}

IRULE
when HTTP_REQUEST {
    if {[HTTP::method] eq "POST"} {
        HTTP::collect 100    
    }
}

when HTTP_REQUEST_DATA {
    set payload [HTTP::payload]
    if {[class match $payload contains "restricted_dg"]} {
        log local0. "Rejecting restricted content" 
        reject
    }
}

HTTP::payload https://devcentral.f5.com/wiki/iRules.HTTP__payload.ashx

HTTP::collect https://devcentral.f5.com/wiki/iRules.HTTP__collect.ashx