First thing is that a character doesn't come up, spot on, perfect, balanced, in one hit of the imagination, as you stroll around the streets.
It takes time. As it takes time, it's clear that the same method is not being used, otherwise you'd finish it in way less time.
So you have different methods.
I usually come up with a name, and that to me immediately, gives me a personality. I don't know if this is a weird form of synesthesia, because along with the names I get colors based on the vowels.
But anyway, I often start with a name, and that gives me one or two personality attributes.
After that I just add to them whatever feels right.
I adjust and hone this based on the history of the characters themselves, and start wondering why they have this personality and I try to come up with actual specific moments, scenes, where I can see this personality trait forming, often containing only kids and teenagers.
From there it just grows. One day I have this idea, inspired by having a dinner with some family friends. Then another day I get another insight into a person's personality through some film or actual conversation.
And I put that still-to-be-known character in a weird situation, like in a speeding carousel, and see how it develops in my head.
Worst ways to create a character?....why should I bother with that? Aren't you, by not using them or thinking about them, avoiding them, which is what you should do in the first place?
Don't bother with the "worst ways".
You're bound to have people consider other people's best ways, their own worst ways.