If Billy states "I think that Bob is a big poo poo head" then that is not slanderous or libelous, because it is an opinion.
If Billy states (for example purposes only) "Bob is a convicted felon who engages in unnatural acts with farm animals" then that is slanderous or libelous if untrue because it is couched as a statement of fact.
Ha! So there's legal obligation to couch your opinions in "I think that...", "In my opinion...", "As I understand it...." etc. Who would have thought that it's a good habit to get into not only for diplomatic purposes, but to ensure you don't get sued for defamation!
(This assumes that the law will recognise the "IMO" and "IME" abbreviations for what they are on the net, and not get anal about the meaning of sentences including such shortcuts.)