If anyone says "Just my two cents" I mark them down mentally as an idiot and a moron. Often abbreviated to the intendedly humorous "just my $0.02". Why do people say this? Two cents is a small and insignificant contribution. So why bother to advertise that your contribution to the discourse is small and insignificant? It's often a lie, said contribution usually being long-winded and repetitive. It's often true, said contribution being banal and lacking any form of insight. But if the latter, surely such self-awareness would be the cause of humble silence, rather than an idiotic and mindless rant.
It's similar to "that's what I think, anyway". Well of course it's what you f--ing think. And that's my two cents.