"Er sieht das Geschlecht nicht."
As a hint, for anyone none german reading here: This is true, but only if no context is given. There are many different Geschlechter and they usually apear in certain context. Tongeschlecht, grammatikalische Geschlechter, Gender or even Geschlechtsorgan. When talking about Geschlecht in your german class, it's pretty obvious, even without the 'gramm.' addition. Context rules out all but one possibility in general. If you still have to smirk about that word, it's your mind, not the sentence.
Generally I agree about the importance of context, but concerning the given example I don't. And its not a question of smirking. You would never say "Er sieht das Geschlecht nicht" in a grammatical context. You can not "see" a grammatical gender, but you could see a sexual organ. You could rather say "Er weiß das Geschlecht nicht", "Er hat das falsche Geschlecht verwendet" or "Er hat das Geschlecht nicht richtig erkannt." All three sentences give the right context by the use of "weiß", "verwendet" and "nicht richtig".
My native German friend's first thought was "Er sieht das Geschlecht nicht." -> what the pregnant woman tells her husband after the ultrasonic. Such as the baby laying in a bad position so the doctor can't see its gender.
If you're talking about grammatical context, most Germans would say Genus, not Geschlecht. Geschlecht would make half of the room snicker, especially teenagers.
Follow up question to rfo/wataya/Menschenkind's discussion...
In English you could say "He does not see gender" with the meaning that whether a person is a man or a woman doesn't influence him (in decision making, in behavior, etc...). Could this be the meaning in German as well (Er sieht das Geschlecht nicht)?