Indicates a harmless level of eccentricity or forgetfulness, usually related to age. Grandpa's plans to build a spaceship have us thinking he's quite dotty.
Pro Tip 2/3
Affectionate Tone
Used in a fond or loving way when referring to someone's quirks. Aunt May is dotty with her collection of porcelain frogs.
Pro Tip 3/3
Not Insulting
Less offensive than calling someone 'crazy' or 'mad', but still be sensitive. He's a bit dotty but means well.