Here are two recent ad hom attacks I've seen in this forum:
"You can spam 50 pages with endless posts copied and pasted from other sources"
"You made a silly statement about the IRS and SSA and got called on it. And if you can't handle that then leaving the thread is probably the best choice to make."
Neither are ad hom. The first is no different than saying "you can say that a thousand times and it still won't be true." That is exaggeration for effect, refers to a person's ACTION and not any attribute of the person's personality, character, or anything else about the person personally.
The second statement is an opinion expressed about the post and again refers to an ACTION, and not anything about the person's personality, character, or any other personal attribute. Criticizing a post is not ad hominem unless it includes a personal attribute of the person making it. The "If you can't handle that. . ." line directly referred to the member's comment threatening to leave the thread because his post was criticized.
Antagonistic? Yes. Expressing annoyance? Yes. Ad hominem, no.
Other examples:
'Your statement is racist or your statement is offensive.' Not adhomen.
'You are racist' is ad hominem. 'You hate black people' is ad hominem. 'You don't care if black people are disadvantaged' is ad hominem. 'Republicans can be counted on to say something like that' is ad hominem.