To me, the funniest line in the whole Liar Liar actually is in the end credit/outtake -- the woman lawyer shouts at Jim Carrey, "overactor!"
my turn...mmm...
1.
A: "What about love?"
B: "Overrated. Biochemically no different than eating large quantities of chocolate."
also toss out two others...
2.
"There's no sacrifice too great for a chance at immortality."
3.
A: "I asked you once if I could be your mother; you didn't want that."
B: "You want to be my mother? You could be my mother; I don't have any mother...so you could be my mother...why would you want to be my mother?"
A: "I don't know...just want to clear things up."
B: "You're my mother; you're my father; you're my mother...you're my whole family...you're even my friend <A> ...you're my girlfriend too."