Justin Bieber doesn't give two craps about the 20-year-old who claims the singer fathered her child -- telling "TMZ Live," the woman is such a ridiculous liar ... she's not even worth thinking about.
TMZ broke the story ... the alleged baby mama -- Mariah Yeater -- can't decide who the father of her kid is ... in fact, just last year, she accused her ex-BF of fathering the same child.
Justin called in to "TMZ Live" today to address the accusations -- telling us it's the first time anything this "crazy" has ever come up ... but he's sure it won't be the last.
Justin Bieber Calls 'TMZ Live'
Baby Mama Schmaby Mama
11/4/2011 2:25 PM PDT BY TMZ STAFF
Get TMZ Breaking News alerts to your inbox