Mr Crisis is right; "runway heading" was dumped from the phraseology years ago but many pilots and controllers seem unaware of it. I frequently get my "climb straight ahead" read back as "climb straight ahead on runway heading". Doh! Admittedly, only in a very strong crosswind does it make much difference what the aircraft actually flies, but it is about time that this irritating little source of confusion was eradicated. An ATSIN might be appropriate.