Elena went from brother to brother. Damon's history with Caroline, Bonnie and Jeremy overshadows sleeping with two brothers. This is a Jerry springer episode.
All the male leads could be considered sluts. Jeremy only recently joined the ranks. All of Jeremy's girlfriends have died.I think he may actually deserve a pass. Jeremy has buried three women he loved.
Caroline went astray by going after Matt, Elena's ex. Possibly Elena's first... If she ends up with Stefan, it will apeear she has some kind of Elena obsession. While her number is higher, still not necessarily a slut. Questionable yes.
Bonnie slept with Jeremy and died. The most moral of the mfg.