Given a 2-coloring of $\ E(K_n)$ such that a red edge belongs to no more than one unique Red triangle, show that $\exists \ K_k \subset K_n$ which contains no Red triangle, with $\ k>\lfloor\sqrt{2n}\rfloor$.
Working through the first few example complete graphs, I've not been able to figure out where this bound comes from. If possible, I'd prefer not to be provided with the proof outright, but rather to be informed relevant results or what might give me some intuition concerning the origin of the bound (What exactly equals the square of double the number of vertices in a complete graph with edge disjoint monochromatic triangles? As far as I can tell, not the number of monochromatic triangles (that depends on the coloring), though that's my first intuition (There are at most $n-\lfloor\sqrt{2n}\rfloor$ edge-disjoint monochromatic triangles for any coloring of the edges, and therefore we can remove one vertex from each triangle, the result will follow.)
Thanks for any hints, I will accept.