Two undergrads in their first year at Cambridge, punting a careful zig-zag course down the Cam, when this American leans over a bridge and yells (insert Texan drawl)
"Hey, steer between the banks!"
If you're going to give advice, it may as well be good. My brother's roomy comes straight back with:
"F**k-off, don't get involved in a land war in south east Asia"
On another occasion, the College porter is standing in the arch at the College entrance when an American lady exclaims:
"Excuse me, is this building pre-war?"
"Madam", he replies, "This building is pre-America"