First thing that came to mind when reading this was head pats
You would love giving William head pats. Will would act like he hated them but secretly love em.
So you'd just do it while walking past him and he'd be like "Bloody luv why must yew do that" you would just laugh at him most of the time.
But when you actually stooped he would frown "Why'd yew stop the pats?" And you would display a large smile "I thought you didnt like them"
Also just image picking William up to the Lion King song (the one where simba is being lifted up by the monkey) this was something that annoyed William "Imma find anothah BoyFreind" He'd say, yall be like "good luck"
William would most definitely blame your shoes for you height but when he wears his shoes the height is 'Natural' just give a head pat and move on.
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Microwave explosion