OTT = Over The Top s a widely-used internet acronym to describe a person's behaviour as being extremely excessive in terms of enthusiasism or over-reaction to a situation.
For more internet acronyms: http://acronyms.thefreedictionary.com/
Note: This internet source gives MANY definitions, and some definitions are unique to certain industries. However, OTT is commonly used on boards/forums and even emails to mean Over The Top.