Polar,
Kudos for dealing with the issue at work!
As for using assertiveness, perhaps how we phrase things depends on the situation.
Tom has been ignored by Harry for months and whenever Tom starts talking to Harry, he is ignored further. If I were Tom, I would say:
"I feel hurt because you seem like you never want to talk to me"
How else can we phrase this effectively?
A work situation might be handled differently than a personal situation. What you say above is good for a friendship or personal situation! At work, management, generally, just wants the job done whether or not Tom and Harry are "friendly" colleagues.
Assuming Tom is only concerned about talking about work issues with Harry, I'd suggest that Tom have a private convo with him. Tom might focus on the effect it has on his work. "Harry we don't seem able to talk to each other and I feel frustrated because we need to work together on [some work issue]."
Another tactic Tom could use if it's just info he needs is to ask for it with lots of people (including the manager, if possible!) right there. And/or Tom could send Harry a memo, "Harry, I need X info from you no later than X date in order to do X [work project]." And
copy the boss on the memo.
If it is a personality clash between Tom and Harry, Tom might say, "Harry, I know we have different styles and approaches. I'd like the chance to learn how
you deal with X, but we don't seem to talk. I feel upset when you freeze me out. Let's resolve this before it starts to affect our jobs!"
Tom could also keep a private diary of his attempts at resolution (what he said/did and Harry's responses). Then, if Tom's attempts to make things work don't work, Tom can go to the boss and say, "On August 28, I spoke with Harry about..." "On August 29, I sent a memo, and you were copied on it..." "On September 2, Harry just walked away when I asked about the data for..." It might not work. But it shows Tom has done his part.
I recommend reading up about workplace bullying. It can be devastating to face it over the long-term. Unless a target can truly come to feel that "Success,
despite the bully, is the best revenge," it's demoralizing to face the bully day after day. (I' speaking from personal experience.)
Good luck, Polar!
A.