I won't go into specifics here of how I might diss Lebron James, but I do sometimes make use of the following chain.
Lebron took his talents to South Beach. South Beach is know for its strong gay community. Gay male sex often involves two specific body parts. Vulgar terms for those body parts can be used to describe Lebron James. Thus, South Beach was the ideal place for Lebron to go if he wanted to feel loved.
Toss in a lot of filthy language and expand on the metaphor further and that's the sort of way I might diss Lebron James and Heat with friends over drinks.
Feel free to use that recipe, but be aware that some people won't take too kindly to it, so choose your audience wisely.