Argument troubles.

Okay, here's the thing. I have two characters: Tyra and Raymond. They're best friends, but Raymond likes Tara, and she knows he likes her, and likes him back but due to complications she acts like she doesn't. They get into an argument about Raymond's feelings. Eventually, Tyra says that she doesn't feel anything for him other than friendship, and Raymond runs off to angst, discovering the plot hook in the process. I've hit a block with this, though. I can't get them to start the argument. The way I see it, Raymond has to do... something that gets Tyra all testy, but it always either comes off as major creepy/rapey (i.e. forcing a kiss on her), or it would seem like Tyra's overreacting (Raymond takes her hand in his while walking, she blows up at him).

In an earlier stage of the scene (i.e. less than 24 hours ago) I had it that Tyra made a bet of some kind with him, and if he won, they would go out, but if she won, he'd stop trying to pursue her romantically. Would that work better?

Perhaps rather than one thing setting her off, it could be just the latest in a line of small annoying things? As in, he's been visibly mooning over her for days, and him trying to take her hand is just the final straw?

Your problem seems to be that you're trying to force your characters to do something that they wouldn't do. Look at your characters, and ask yourself, "Would either of these two characters engage in this sort of argument?" You have to look at how confrontational they are and how comfortable they are in their interactions with each other. Would they truly speak that freely to each other, or would they beat around the bush, or avoid the topic altogether and make the issue about something else? Another thing you have to look at is why would they have this argument? What do the characters hope to gain from having such a discussion? Is it really important for your character to tell the other that she has no feelings for him?

Instead of trying to force your characters to fall into the situation you want, try to figure out what your characters would do instead? What are their motivations and how would they, on an individual level, achieve their goals? How much does Raymond love Tyra? To what lengths is he willing to go to show his love? How would Tyra react to these shows of affection? Would she get mad and want to start an argument? Or would she be the kind and caring friend who just wants to set him straight?

Keep in mind that a lot of arguments aren't just straight forward. You'd probably have a lot of confused feelings, and people bringing up points that have nothing to do with the real issue, going off on tangents, or saying things they didn't really mean to say. So maybe the argument doesn't start out about Raymond's feelings. Maybe it starts off about something Raymond did, that's annoying. Then it becomes about Tyra needing her personal space. Then maybe it becomes about something childish Tyra did in preschool, which really has nothing to do with anything. Eventually, they both get madder and madder, bringing up stupid things the other person has said or done, that alternate between touching upon the real issue and completely missing it. Suddenly, Tyra can't stand it anymore and her true feelings come out.