Is this an ad hominem or what?

I hate people who respond with: "Says the guy who...", "You're one to talk.", "Look who's talking?", and "Says who?". This goes to ignorants who disregard opinions from users who have an anime character as profile picture regardless of how reasonable their comment is as well. They don't need to show their real life face nor being a non hypocrite to write such comment.

If you say you don't intend to offend anybody by saying this, then explain why this comment is necessary.

If your intention is simply find it funny, then keep it to yourself because your laughter serves no purpose other than to satisfy your personal joy.

First I want to address the content of what the person is saying... the people who say things like "You're the one to talk."

There does seem to be an implied argument if not explicit when someone uses one of these phrases. This would be a ad hominem (tu quoque) . For example:

Billy eats a dozen doughnuts a day. John point out to Billy that this is not a good lifestyle decision. Billy retorts with "Says the guy who is currently eating cake." The implication here is that John's observation carries less weight, that is, the conclusion that eating a dozen doughnuts a day is a poor lifestyle choice doesn't follow from the "argument," (implied: premise(s) are the obvious health results). When in fact, it does.

It can also be harmless and someone is simply pointing out the irony in the situation. In the above example, it might be that Billy agrees with John, but it is ironic that John happens to tell him this as John is stuffing cake down his cake hole. If John had a sense of humor, he would have to find this funny or at least appreciate the irony in the situation. As someone who writes comedy, I would have Billy say something other than "Look who's talking," because that is generally seen as abrasive. Perhaps Billy can simply say "How's your cake?"

Now, in terms of the person that posted that (the person who hates people who respond with...), they appear to be expressing an opinion rather than making an argument. They are making an assumption that the opinion is being disregarded, where as I explained previously, this may or may not be the case.  So I would argue that their opinion (claim) is unsupported.

Dr Bo is correct; it's typically not trying to make an argument.

However, sometimes, people do try to dismiss arguments based on personal characteristics.

Eugenie: You really need to stop drinking. It'll damage your organs, especially your liver.

Merrida: Says the one who got wasted at the party yesterday.

The implicit argument is that an observation is only valid if the observer is completely innocent of themselves. That's an ad hominem (tu quoque) because, as the example shows, Eugenie's remark - that alcoholism is dangerous - does not become false because she got drunk the day before. Medical facts are independent of individual behaviour. 

If someone uses logic like "you have an anime avatar, your opinion is invalid" then that's normally just a joke referencing the often-degenerate behaviour of those with such avatars. However, if it were serious, it'd be ad hominem (abusive).