Shikubokubo

Don't get me wrong, a guy who is able to express his emotions isn't a bad thing. The problem is that guys tend to express their emotions in a more physical way, rather than verbal. It's like JetKL said, there's a complete lack of realism when a normally stoic character has sex and is then suddenly declaring his undying love in a way that no person ever would. This is from a oneshot I read recently. The story was good, it gets to the lemony-goodness and then... BAM! Not only is it very OOC for this particular character but it's completely unrealistic and for me that's a huge turn-off. If it had been left at "Uchiha's are never unfaithful" it would have worked fine.

On a similar note, something I really hate when reading a yaoi fanfic is when one (or both) of the 'guys' (I use this term loosely because sometimes I wonder whether or not it is actually a guy), either after or during some hot, steamy mansex, will use dialogue that sounds like he is reciting his homemade wedding vows. Now I'm all for some romance, but guys do not talk like that.