to keep talking about something again and again because you think it is important; preoccupied or obsessed with an idea
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She has got a real bee in her bonnet about people keeping their dogs under control.
Radek has a bee in his bonnet about playing games.
I got a bee in my bonnet about swimming. I just wanted to go swimming all the time.
My sister never stops talking about dieting - she's got a real bee in her bonnet about it.
have a bee in your bonnet (about something/about doing something)