What Do You Mean, It's Not an Index?

Either the work or the audience plays up something in the work as something it's clearly not (mostly).

When done In-Universe, it's often Played for Laughs (see Does This Remind You of Anything?), Rule of Cool, or the writers just having fun. When done by the viewers, it can be Fan Dumb, or it can be them legitimately assuming something if the show unintentionally makes the thing look like the trope (see Unexpected Reactions to This Index).

Since titles in this format and figuring out whether to use "It's ____" "It's Not ____" can be confusing, remember this: The "It's ____" part is what was originally intended by the work.

Closely related:


http://tvtropes.org/pmwiki/pmwiki.php/Main/WhatDoYouMeanItsNotAnIndex