Latin for why so serious

cur tam serius

Note that serius is masculine singular.

Please read this.

cur tam seria
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. . . or if a case is feminine when you needed masculine

How did you come to know that it is masculine, for it may be in plural:
Why (are we) so serious.
Besides there are some people that are speaking about themselves as 'we'.
This thing cannot be translated in any language without seeing the picture first.

I don't know that the requester wanted masculine singular, I assumed it.
That's I why pointed it out to him. If he wants another gender or number,
then I hope he will ask for it.