hob·by·horse 
/ˈhɑ:biˌhoɚs/ noun
plural hob·by·hors·es /ˈhɑ:biˌhoɚs/ noun [count] 1 : a subject that someone speaks about or complains about often
▪ Once he gets on his hobbyhorse and starts talking about taxes, you can't get him to discuss anything else. ▪ She's been riding that hobbyhorse for months. 2 : a stick with a horse's head at one end that a child pretends to ride
▪ Once he gets on his hobbyhorse and starts talking about taxes, you can't get him to discuss anything else. ▪ She's been riding that hobbyhorse for months.
