To express "I'm horny" in Japanese, the phrasing depends on the level of formality and context. A casual and direct way to say it is エッチしたい (ecchi shitai), which means "I want to do something naughty." Another playful expression is ムラムラしてる (mura mura shiteru), which describes feeling aroused or sexually excited. For a more euphemistic or less direct approach, you might say 気分が高まっている (kibun ga takamatte iru), meaning "I'm feeling heightened emotions," though this is less explicit. These phrases are best used with caution, as openly discussing such feelings can be considered inappropriate in many social situations in Japan. Context and the relationship with the person you’re speaking to are key to choosing the right expression.