Heard over the past two nights over a LON frequency dealing with oceanic traffic I/B from US, after extended comms requiring level changes due moderate trubulence:
US a/c (eastbound):
"Errr, London, the chop is much lighter at this level".
Female ATCO (sounding fascinated
):
"Yyyepp!"
This morning, very much same occurence, apparently the ride at FL390 wasn't too smooth, with some flights again requesting level changes:
US a/c (eastbound again):
"London, the ride is smoother at FL370, thanks a lot" ATCO:
"Oh, that's OK, sir, that's my job!" 
Priceless...