Or ask them a question and see which ones explain the answer whilst waving their hands about in "I went like this, he went like this, I was like where'd he go? He was like Where'd who go" Top Gun stylee.
Or in the case of Harrier/F3/Chinook/Anythingdifferenttowhatyoufly mates just wait for them to introduce themselves as "Hi, i'm Bloggs, I fly ....."