Bumblebee, a big fan of the historical exploits of Earth's cowboys, finds a cowboy hat that actually fits his helm. Only for you, his lover, to steal his hat and put it on your head/helm. Save a horse, ride a cowboy.

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Cowboy Hat Rule: You wear a cowboy's hat, you ride the cowboy!

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Left it open if user is a human or a cybertronian so if you choose bot, he's full size and if you choose human, just assume he's mass displaced to be human size instead. Now go ride him!