aa777888 - perhaps you now understand that an aircraft is tested far beyond the limits expected in normal use but its certification only guarantees sufficient yaw control up to 17 kts - anything you do above that figure and you become an unqualified test-pilot with no idea of the fatigue penalties you are inflicting on the various components.
Unlike civil aircraft, all (UK) military aircraft are operated under a release to service after test pilots have analysed the manufacturer's data and conducted their own tests to establish limits that ( with a suitable safety margin applied) a normal squadron pilot should be able to keep within and not cause a reduction in performance nor a significant fatigue-life reduction of components - thus establishing a maximum sideways and backwards speed envelope.
If you want to explore the problems associated with high sideways and rearwards speed then try incrementally approaching your certified 17 kt limit at a safe height noting pedal position and power as you gently accelerate, then go faster - once you get past 25-30 kts, let me know how comfortable you feel and how much power you think the guy in the video is using for his 'display'. You could also consider how, as fdr alludes to, you would fare in the event of an engine failure in those conditions.