“I can't stand it when a man doesn't trim his nails.”
You're talking about men with a group of girlfriends. Everyone is talking about what kind of men they don't like. You tell them about a quality that you don't like in men.
I can't stand it when a man doesn't trim his nails.
Talk about something you don't like at all with the phrase "I can't stand ___":
I can't stand olives!
I can't stand being apart from you for so long.
I can't stand people who make racist jokes.
I can't stand to see an animal in pain.
You can talk about other people with this phrase as well:
Some people can't stand losing.
She can't stand it when people talk while they're chewing their food.
It's not that common to use "stand" this way in positive sentences. Instead of saying that you can stand something, say that you can "tolerate" or "handle" it:
A: Do you like rap music?
B: Yeah, it's not my favorite but I can usually tolerate it.