Does it cause any flu or brain damage if i washed my hair with cold water in cold weather then i dried my hair with hot air?

No difference: There should be no flu symptoms nor brain damage arising from washing one's hair in hot water in hot weather and drying it with cold air, nor from washing one's hair in cold water in cold weather and drying it with hot air. Likewise, it doesn't matter if hair is washed with hot water in cold weather nor cold water in hot weather, and it makes no difference if hair is dried with hot or cool air.