Herkes beni deli sanıyor.

Because herkes is grammatically singular in Turkish.

So Turkish treats it like English everyone or everybody:

• Everyone thinks...
• not Everyone think...

That is why the verb is sanıyor, not a plural form.

Because beni is the accusative form of ben.

Here, beni is the direct object of sanıyor. The sentence is about what everyone thinks about me, so Turkish uses the object form:

• ben = I
• beni = me

So:

• Herkes ben deli sanıyor ❌
• Herkes beni deli sanıyor ✅

Deli is the word that describes what people think I am.

In English, we would usually say:

• Everyone thinks I am crazy
• or Everyone thinks I’m crazy

In Turkish, after a verb like sanmak, you do not need a separate word for am here. Turkish can simply place the describing word before the verb:

• beni deli sanıyor = thinks me crazy

So deli is functioning as a kind of object complement or predicative word describing beni.

It can be either, depending on context.

Turkish often uses the same word both as an adjective and as a noun. In this sentence, deli most naturally means crazy in the sense of describing you.

So:

• beni deli sanıyor = thinks I’m crazy

It does not need an article like a here.

Sanmak means to think, to suppose, or to assume.

But it often has the nuance of believing something to be true, possibly mistakenly.

So Herkes beni deli sanıyor is a bit like:

• Everyone thinks I’m crazy
• Everyone assumes I’m crazy
• Everyone takes me for crazy

Compared with düşünmek, sanmak often feels a little more like an assumption or impression.

Because Turkish often uses the -iyor form for things happening now or for a current ongoing situation.

So sanıyor can mean:

• is thinking
• thinks
• currently considers

In this sentence, it does not have to mean that people are literally in the middle of thinking at this second. It can also describe the present situation in general:

• Right now, everyone thinks I’m crazy

It comes from the infinitive sanmak.

Breakdown:

• sanmak = to think / suppose
• remove -mak → san-
• add the present continuous suffix -ıyor
• third person singular has no extra ending here

So:

• san-ıyor = he/she/it thinks, is thinking

The vowel is ı because of vowel harmony.

Turkish normally puts the verb near the end, and that is what happens here.

A helpful rough structure is:

• Herkes = subject
• beni = object
• deli = complement describing the object
• sanıyor = verb

So the pattern is roughly:

• Everyone me crazy thinks

That sounds odd in English, but it is normal in Turkish.

Yes, Turkish word order is flexible, but the emphasis changes.

For example:

• Herkes beni deli sanıyor = neutral
• Beni herkes deli sanıyor = puts more focus on me
• Deli herkes beni sanıyor ❌ = not a natural way to say this

So you can move parts around, but not every order sounds natural.

Yes. That is a more explicit version.

It literally means something like:

• Everyone thinks that I am crazy

Breakdown:

• benim = my / of me
• deli olduğumu = that I am crazy

So the two versions are related:

• Herkes beni deli sanıyor = shorter, very natural
• Herkes benim deli olduğumu sanıyor = more explicit, more clause-based

Both are correct, but the original sentence is simpler and more conversational.

They overlap, but there are differences in feel.

• sanmak = think, suppose, assume
• zannetmek = very similar to sanmak, often also assume/think
• düşünmek = think, reflect, consider more generally

In this sentence:

• Herkes beni deli sanıyor sounds very natural
• Herkes beni deli zannediyor is also possible and similar
• Herkes benim deli olduğumu düşünüyor is possible, but a bit more neutral or analytical in tone

So sanmak is a very good choice when talking about what people take someone to be.

Yes, from an English point of view, you can think of it that way.

English needs:

• I am crazy

But Turkish often does not need an explicit to be in this kind of structure, especially inside expressions like X’i Y sanmak:

• beni deli sanıyor = thinks me crazy = thinks I am crazy

So the idea of am is understood without being separately stated.