Well, other than the standard questions about who packed my bags, etc., the first time I came to London with a friend, and we said we were tourists, the immigration lady was pretty rude about asking exactly what our plans were, which places we would see, etc., and seemed pretty unsatisfied with the usual London Tower, Westminster, etc., asking "and what else?" and was very curt, which was unexpected for me, since I had never travelled outside the US before (I certainly didn't mention I was there to meet someone in person that I had been talking to online!) I guess I just thought if you said you were a tourist, then that would be that!
The other times, they were much nicer, though when I said I was here to take a connecting flight to Newcastle to see my fiance and meet his family, I got a bit of a lecture on how I would need a visa in order to live here, etc., but I explained that I was only here for a week and planned to observe all the rules. And then she asked where my fiance was at the moment, and I said "probably right outside that door, am I free to go??" and she just smiled and let me through!