How exactly is it impossible though? Could you demonstrate it with (preferably) some premises or something similar?
I've found that many attempts at 'debunking' the idea (which are actually questions that are 'set', in their inherent nature and direct phraseology) of a God allow a supposed 'omnipotence' to be 'disproved', while wholly being based around that original (preconceived) concept in the first place (see: bias).
A very common approach is to pose the following question: "Can God create a stone so heavy that even He cannot lift it?"
If ones answer to the question is "yes", they would generally conclude (or sometimes surmise) that this means that either he ceases to be omnipotent in at least 2 ways: 1.) He cannot create the stone to begin with and 2.) he cannot lift the stone what he created.
If ones answer to that question happens to be "no" then it directly implies that he just, in general, lacks the ability to either 1.) lift the stone or 2.) create the stone to begin with
As demonstrated here, both questions are inherently and intrinsically a gateway to 'disproving' any supposed omnipotence that X deity has/possesses. Moreover, notice that the usual answer to the question is NOT made by the deity in question, but rather, by the individuals proposing the question to begin with. As aforementioned, any amount of answers (as far as I know) will ultimately preclude the possibility of any supposed 'omnipotence' (either real or imagined). However, I do not necessarily believe that a supposed 'failure' from a deity to amount to some avowed criteria (in this case, creating and lifting a heavy stone, said stone being "so heavy God cannot lift it") demonstrates a lack of omnipotence, especially when the question, in its very nature, is solely reliant human answer. Others often resort to other (similar) tactics, which are, incidentally, mere variations of the question above (however, they are usually phrased to become a statement, rather than a loaded question). A very recurring and common statement is "IF God loves EVERYONE, he MUST love me, after all, God doesn't want anyone to go to Hell (smirk)." Said remarks are generally used as a backhanded way to attack someone's own argument without having to substantiate their own argument at all.