Nope. Hate it. One of the big selling points of getting in with your guys on S4s was not having to negotiate. I'm very tempted to get someone else to negotiate my next car. Best experience ever was for my wife's current car; did it all via e-mail over the course of a morning.
Doesn't Tesla sell direct to customers? Since you said you were interested in a Tesla anyway for your next car, that seems to be yet another compelling reason to buy one.
I hate haggling myself. When I quote people prices, I almost always quote exactly the price I want. At times I've had people try to chew me down, but I explained I don't highball my initial quote like lots of others do. Oddly enough, lowballing quotes to get jobs seems to be another tactic often used by those in the home improvement business. Once they get the job, they'll claim all sorts of unexpected things are happening and try to charge more for it. Happened to me more than once. After the second time this happened I told them I signed a contract. Either you do the job at the quoted price or you refund ALL my money and I'll find somebody else. In the end they aren't happy since they'll likely lose money, but most will finish the job at the quoted price rather than refund all the money, often leaving them with an even bigger loss if they've already done half the job. I still remember one of them leaving, moaning to me "I lost $3,000 on this job". I simply told him he should have initially quoted me a price he would have made money on instead of playing games.