I tend to say 'One-Eighty' in that circumstance, which definitely isn't the correct format for a heading or a level, and anyway, headings and levels have no relevance on the ground unless you're about to depart - as you said, it tends to be used after landing. Certainly never had anyone misinterpret it, even foreign pilots with poor english.
'Turn around and go the other way' is far too much of a mouthful.