I don't think I have ever seen another BMW driver wave at another one unless they own an awesome e30 or 2002. The only group of cars I see that wave at one another other than Harley owners are Mini owners.

My parents bought a Mini when I was in college and I had it for a week when my 5-er was getting the Dinan stuff installed and every Mini I saw the owner waved to me.

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Jeff
Current:
'07 Jeep Wrangler
'06 BMW X5 3.0i

Former:
'12 WRX; '08 WRX; '06 BMW X5 4.8is Dinan S1; '02 BMW 530i Dinan S2