Decal: A good subset of Tesla owners apparently consists of die hard fans who are often characterized as toxic and exclusive
Caption: Original post was removed by moderators for not censoring the license plate
Mind reading: The joke is that the Tesla driver is aware of the toxic behavior exhibited by other Tesla owners, especially in relation to Tesla executive Elon Musk, and is preemptively denying such associations
edit: mfs on this site will rly downvote anything huh 😭
The implication is that the poster wondered why the owner bought a car associated with Elon. The decal answered that question, giving the impression that the owner read the poster's mind.
Back in 2014 my graduating physics class was split down the middle between dudebros who wanted to be him and people who thought he was a con artist due to the utterly ridiculous physics statements that he'd make.
So basically this decal identifies the owner as the sort of silly person who thinks settling other planets isn't the punchline of a joke.