I thought about this question a lot when I was on my way to identifying as trans*. These examples are how I tell the difference, so I'm using all "I" statements, but this can be generally applicable to anyone.
General dislike: I feel connected to my body, but I hate my body. (i.e: I look in the mirror and hate that I've gain/lost weight. I lament this fact, but still feel that my body is unfortunately my own)
Dysphoria: You feel disconnected from your body, yet you may like or dislike your body. (i.e: I look in the mirror and appreciate my body on some days, but feel like I'm checking out a stranger in my reflection. to further explain, if I saw someone on the street with my shape and parts, I'd think they're hot/attractive/nice looking. However, this body is not for me, and yes, thinking about that makes me quite sad.)
General Dislike AND Dysphoria: You feel disconnected from your body and you think your shell is unappealing IN GENERAL. (i.e: i hate what I see in the mirror because I find it unappealing, and I feel disconnected from what I see, which typically compounds my level of hatred)
Sidenote -- I do not believe dysphoria is limited to just trans* people. What makes gender dysphoria different from other forms is that the thought of "My body is not my own" is compounded with the sincere need and belief to present as the opposing gender, which, when practiced, relieves the pain of dysphoria.