According to

[ROBINDESBOIS]

What's the opposite of according to?

[Rusty]

Context is needed, but some of these might do:

in disagreement with
inconsistent with
incompatible with

[Awaken]

I'm not sure there is a true direct opposite. Rusty's choices are the same I would say, but they are not really "opposites" to the phrase itself. Can you provide some context for us?

[poli]

You can say: not according to (me).

This term is often used when you disagree with someone.

What's the opposite of segun.

[ROBINDESBOIS]

En desacuerdo con el titular

[Rusty]

in disagreement with
at variance with
at odds with

opposed to

[marmoset]

How about "contrary to"?

[ROBINDESBOIS]

What about disagreeing with?

[poli]

I prefer Marmoset's contrary to. This works most of the the time. Some of the other choices (like my not according to) don't always work in all circumstances. Others sound awkward.

[marmoset]

:)

It came to me suddenly while washing the dishes.