Much Ado About Nothing
How we cite our quotes:
You will never run mad, niece.
No, not till a hot January. (1.1.93)
"Run mad" here refers to catching what Beatrice calls "the Benedick" – essentially going crazy for love. For Beatrice to "catch the Benedick," she’d have to be in love, which she says is as likely as a hot January. That is, "when hell freezes over." (Still, she will catch "the Benedick" soon enough.)
Then is courtesy a turncoat. But it is certain I am loved of
all ladies, only you excepted; and I would I could find in my
heart that I had not a hard heart, for truly I love none.
A dear happiness to women! They would else have been troubled
with a pernicious suitor. I thank God and my cold blood, I am of
your humour for that. I had rather hear my dog bark at a crow
than a man swear he loves me. (1.1.124)
Note that both Beatrice and Benedick say they’ll never love anyone. This little spar is likely saying "of course we’ll never love each other." Invulnerability to falling in love is a point of pride for them both.
That I neither feel how she should be loved, nor know how she should be worthy, is the opinion that fire cannot melt out of me.
I will die in it at the stake.
Thou wast ever an obstinate heretic in the despite of beauty. (1.1.230)
Benedick hates love, and he’s known for hating beauty. Beauty can’t move him to love, but perhaps some more meaningful trait in a girl (like how witty she is, and if she’s named Beatrice) could move him.