Sometimes it is simply that the rhythm of two names sounds better in one order than the other. For example, Tom and Jerry sounds better than Jerry and Tom. There is no implication that one is more important than the other.
Well, you *could* be a sad loser, or the speaker thinks the order is appropriate because of the value of your respective contributions, or maybe he's saving the best for last. Not every choice is going to meet your definition of obvious.
Answers & Comments
It means they hate you
Sometimes it is simply that the rhythm of two names sounds better in one order than the other. For example, Tom and Jerry sounds better than Jerry and Tom. There is no implication that one is more important than the other.
Well, you *could* be a sad loser, or the speaker thinks the order is appropriate because of the value of your respective contributions, or maybe he's saving the best for last. Not every choice is going to meet your definition of obvious.
that theyre just thanking you and sonneone else for sonnething you did
That's a pretty vague question. If someone uses your last name, they use your last name. They're referring to you. What's the big deal?
In your example, it means they are thanking you.