I'd wave at them, and ask for some pictures with them to put on Facebook.
*The article "an" is just used for vowel-sounding words. U is a vowel, but it has the y-sound. The X in x-ray has an E-ish sound, so it gets to hang out with "an." So it's pretty much "an" is used for words that have an initial vowel sound, and "a" is used for words with initial consonant sounds. Like eulogy and euphemism begin with an e, but sound like a y... if that makes sense. (How'd you make the text smaller?)
What would you do if Tom Hanks asked you to go on a cross-country run with him?