What does it feel like for a male to be horny? I agree with Jason, Hardcock and Henry.
I can feel the air rush into my lungs. Smells smell stronger. I see better. I notice details in people and places that I never saw before. Things become interesting. I balk at the phrase "spidey senses", but that's pretty much what it's like.
Have you noticed that horny men make the best writers. They're more engaged with the world. (Is that why you chose your handle, Henry?)
Can you tell when it's going to get hard? Yes. Mine gets hard every three minutes. I use it to boil eggs.
Sorry, SpoiledPrincess, that's a joke. In fact, you can only predict when it's going to get hard to the extent that you can predict where your eyes and thoughts will wander. My dear old subconscious, bless it, stays alert to anything sexual, whether it be inside my head or before my eyes. It's arousal radar. And a stiff dick is the blip on the screen that shows it found something.
Women have hormones, too, and are just as constantly horny? So, you're wet every three minutes? Do tell...