How to Report Abuse on YouTube
(Note: you must be logged in to flag videos and comments.)
To report a video:
Click the flag shaped icon in the lower right corner under the offensive video. When your mouse is hovering over it, the icon will read "Flag as inappropriate."
To report comments:
Click on the icon with the flag to the right of the comment you want to flag as spam.
More information about: YouTube's Content Reporting and Removals