A real tailslide is nothing more than an aerobatic maneuver where the plane pulls up into a 90 degree climb until it stalls and then falls back to earth with its tail pointing downward. Once some speed is gained, hard rudder input brings the nose back down.
I cant imagine a SINGLE instance where this maneuver would be of benefit in ACM since at the top, the enemy is completely defenseless. The people you were talking to may be referring to something else but a real tailslide is strictly for an airshow not for combat.
-Ding
PS...I remember a contest back in WBs where you were supposed to film (take picture?) of yourself using smoke and doing a tailslide. Was pretty cool.