My parents are seriously gross! why do adults sometimes forget how old they are?!?

My parents seriously need to stop being all over each other. Yesterday I walked into the kitchen after school and find my dad on top of my mom (slobbering all over her stomach) on the kitchen table...i was like wtf?! can they stop acting like teenagers? they should try to hide their weird ual urges...i once walked into my parents room to ask my mom where the air brush was and i hear my dad yelling, "****, close the door"...it's like anytime I want to ask something or whatever they are always doing something teenagers do not 38 year olds. Last week while we were watching a movie my dad slipped his hand in my mom's pants, patted her private part and said, "mommy, mommy" WTF?! seriously they're like addicts. ewww. Why do grown ups act like they're still teenagers? how can i stop them from doing this? should i tell my mom i think my dad is taking advantage of her?