Yes, I encountered some anti-American sentiments when I was at law school. Mostly, it manifested at lectures/tutorials when we discussed substantive legal principles and there would always be one person who would debate against American policies and applications under the guise of comparative analysis. There were also stabs at semantics. But, I always gave back as good as I got so, I did not find it irksome at all and attributed that to overzealous law students and I think ignorance also contributed to that. Generally, the British are a very friendly lot and I have yet to meet one who would strongly or directly confront me with anti-American slurs or behave in an untoward manner just because I am American.

It can be different in the continent however, when some locals pick up on the American accent. There have been occasions when some would talk behind my back with derisions like "obnoxious American" or "go home, foreigner" or "stupid American, we don't want your dollars here" etc. Something like the Chevy Chase movie "Lampoon's European vacation". But, it's not often and it depends on where I go. I get a kick out of the situation when I retort loudly, but politely, in the local vernacular and leave them with red faces all around.