These sort of conversations are almost always futile, anyway. You can say "I was listening to X before anybody knew who they were" but the fact remains that becase you've heard of them, then lots of other people already have and were listening to them before you. The only exceptions would be
(i) They're a band local to you who later make it big. I went to see The Cooper Temple Clause a couple of times in Reading, for example. I also saw Hard-Fi before the NME picked them up, although they were starting to get publicity by then... and to be honest I thought they were a bit rubbish.
(ii) You happen to see them supporting an artist you like on tour. But to be honest, the fact that they've got a decent support slot means that there must be a whole bunch of people loving them already. I saw Hundred Reasons supporting Muse, for example, but they were pretty big then even though they'd only released one EP.
(iii) You're an obsessive music nerd who posts on every local music site you can, just so that you can claim you were listening to X before everybody else was. You probably boast to your friends about how you were hanging out with Conor Oberst back in 1998, because you think that makes you cool. It doesn't. Conor Oberst is a whiney little scag.