When your mind and body becomes so overwhelmed with such ecstatic joy while delivering the father of the groom speech that you yell out at the end "I'm having a mental ejaculation of joy" and then drop the mic.
When you have a roaring hot diarrhea of fire the day after having consumed very spicy foods, such as a Vindaloo curry. This usually happens first thing in the morning, mere minutes after you wake up, and it stings even worse going out than it did coming in.
Man, last nights curry was friggin' delicious, but it resulted in a painful Vindaloo evacuation early this morning.
Premature eloculation is the what happens when you get in your car, and you reach over to unlock the door for someone, and they try the handle too soon so you have to unlock it again, and they try it too soon again so you have to unlock it yet again. Their repeated attempts to open the the door too soon is known as premature eloculation.