I tried putting my two male leopard geckos Bahamut and Jubjub together once a long time ago before I moved out to B.C. to attend university, and before I had heard about the male aggression thing in lizards. We placed Bahamut in the 35 gallon tank Jubjub was living in at the time and Jubjub didn't take it that well. Not surprisingly, he was the only aggressor while Bahamut wasn't aggressive at all. My brother-in-law assumed that was because Bahamut was really female. Which wasn't true because first of all, he was hatched male; second, Jubjub would probably have tried to mate with him if he were female, and that didn't happen; third, although they are rather small, Bahamut does have some hemipenal bulges. I assumed the one-sided aggression was due to Bahamut being in Jubjub's territory. If it had been the other way around, Bahamut would probably have been the aggressor. The age difference might also have played a role. In any case, we left them together for a day and since then neither of them have seen another gecko at all.[/QUO
Very dangerous to put 2 males together, they could kill each other. It is best if they are the same size and weight but there are exceptions to this rule.