Just to make it clear, this means I show it to you.
And I show you (to someone) would be:
In Thessaloniki, many people (especially the older ones) tend to replace μου, σου, του & της with με, σε, το(ν) & τη(ν) respectively. For example, one can hear both Σου δείχνω τη φωτογραφία and Σε δείχνω τη φωτογραφία in Thessaloniki.
This happens because the dative (a case used in ancient Greek for indirect objects of verbs) gradually disappeared over the centuries and was replaced by the genitive case in the South and by the accusative case in the North of Greece. Eg:
Σοιδίδωμι τὴν ἐπιστολὴν (= I give you the letter) -> σοι (= you, indirect object): dative, τὴν ἐπιστολὴν (= the letter, direct object): accusative, became
Σεδίνω την επιστολή in northern Greece &
Σουδίνω την επιστολή in southern Greece.
Nowadays, the southern version is considered to be the grammatical one, but that doesn't really matter for the proud inhabitants of Thessaloniki. :-)
I think lojle was correct. If they use σε in Thessaloniki, it's all the more reason to use σε δειχνω.
Why is "I show it to you" wrong?? (The comments are about Thessaloniki and the language, that is spoken there... but i think, this is a problem, that affects the English language.)
"σου το δείχνω"... here is το the accusative. But in "I show you" is "you" the accusative (!) In this case "σου" must be the indirect object (= to you).