Ray..pls mention using what device/module you want to achieve this, if its IPS/SSM then it may be easily done by enabling signature
If its ASA then please use the sample config I designed for you
configure terminal
regex block-website-regex ".\youtube.\com"
class-map type regex match-any block-website-class
match regex block-website-regex
exit
policy-map type inspect http block-website-pm
parameters
match request header host regex class block-website-class
drop-connection log
exit
exit
policy-map global_policy
class inspection_default
inspect http block-website-pm
exit
Do rate if helpful...
