Opposite of "witty"

So today my friend gave a really good line about leftovers. I personally thought it was very witty. I tried to give a witty response, but it ended up being kind of lame and not making much sense, hehe.

I thought to myself, "I tried to be witty... but I ended up being _". And then I couldn't fill in the blank. I wanted to say corny, but I wasn't sure if that was correct. So what is the opposite of witty?

The opposite of witty could be witless but in the following example

I tried to be funny but I ended up witless

It simply doesn't work. Moreover, witless suggests that the person lacks basic intelligence, someone who doesn't have a clue, and is dependent on another. Overall an ambiguous and very negative adjective which I would generally not recommend. On the other hand...

I tried to be witty but I ended up witless

is actually quite witty IMHO, and works because of the preceding adjective. But as a stand alone, and for the reasons I explained above, I think witless is best avoided.

Normally this type of situation—a line that comes off as being unfunny (or unoriginal)—is said to fall flat.

I tried to be witty but I ended up falling flat on my face.

I tried to be witty, but it fell flat

A punchline falls flat when it fails to receive the expected reaction from the listener i.e. laughter.

Depending on the lack of positive response from an audience you could say a comedian was a complete fiasco and his act a disaster.

Most of her jokes fell flat and her act was a disaster

Of course, the most obvious solution is unwitty. It fits perfectly.

I tried to be funny but I was unwitty
I tried to be witty but I was unwitty

Wiktionary says: unwitty (comparative more unwitty, superlative most unwitty) (chiefly archaic) not witty; without wit; silly

I would think either dull or dry.

Dull: lacking zest or vivacity

Dry: not showing or communicating warmth, enthusiasm, or tender feeling