DD is 6....recently she has taken to surpising me when I least expect it....jumping out and saying "boo" in a really sharp and loud voice. Every time it is when I have been alone for some time..so totally not expecting it....the other day she did it wile I was in the bath and its horrible!
Just now I was cooking...sharp knife in hand and boiling water nearby and she did it again! 
I had a terrible shock and jumped about a foot in the air....burned my hand and totally lost my temper...roared at her which I NEVER do...not really hard or anything but feel so bad!
I HAD told her previously not to do this as it's bad for me....and can be dangerous...plus I am a highly strung type...easily rattled and I think she knows this and likes the effect!
I have told her I am sorry for the scary roaring...but that she mustn't jump out on people like this...is that reasonable or is it quite acceptable to jump out on people?