Electric toy trains

knockers  See tits, hooters, bazookas, bazongas... same thing.  Knockers have to be kinda big to deserve being called that.  Lil titties are better addressed as mosquito bites or zits

 Like electric toy trains, knockers were originally designed for kids, but are mostly enjoyed by grownups. 

On fleek

On fleek:  the quality of being perfect, or on point i.e. Zayn Malik Zayn is on fleek due to his ability to appear perfect at all times.

1. adj. hella; on point  2 adj. very good 1. My eyebrows are on fleek  2. James' personality is on fleek