Objective theory of contracts assignment

On March $4,2004,$ the Louisville Scene, an online service of the Louisville Courier$-$Journal, ran the following report:

According to the New York Post, George Clooney wrote the following in an appeal to his Hollywood friends.

I will start with a warning $-$ I$\text{'}$m asking for money so you might want to stop reading and pretend you never got this letter. My father, Nick, is running the $U$ House of Representatives in Kentucky's $4^{th}$ district. He's the Democratic candidate. There's a limit to what anyone can donate to a campaign. Otherwise, I$\text{'}$d pay the whole thing. So I$\text{'}$m writing you in hopes of scaring up some cash for his Congressional bid. If you can't or don't want to$,$ I understand. However if you can $-$ I$\text{'}$m having a cocktail party at my hose on March $6$ at $7$ pm$.$ It's a benefit so there will be entertainment, hors d'oeurves and booze. And I'll wash your car every week till it's paid off and Armorall the tires om a toga. Hope to see you there, George.

Clooney further wrote that the minimum contribution is $$500$ and the maximum $$4,000.$

Is Clooney's handwritten an offer that could bind him to wash cars in a toga if accepted?

Assume, when asked, Clooney says he never intended to enter into a contract. I was just joking. What legal effect does his subjective intent have on whether or not it was an offer?

How would the determination of whether he was joking be determined?