My son always (from age 4 to elementary school) had this weird love for being dressed in a dress shirt and a clip-on tie. He wants to wear it very often, both to more dressy occasions (parties etc..) but ALSO randomly when playing at home - even when playing ball, not just playing at having a party.
He got the idea from the costume he once wore for a preschool show.
But that show wasn't his favorite and thus I don't think it's transferring good feelings from the show to the attire.
It does not seem to be imitation (the father never wears ties to work, nobody he knows wears ties in even party situations, no kid acquaintances/friends wear ties).
What possible cause could there be for this?