I've 'met' him maybe 2 or 3 times, when I say 'met him' that basicly means walking past him and saying hi or asking for a pic/autograph. In my experience he's always been really introverted and quiet. I'm pretty sure he said nothing at all when I asked him for an autograph and a picture (two seperate incidents) but just did what I asked for. The first time I bumped into him was the most memorable experience
I went to my very first tennis tournament to see Seb play and when I entered the grounds, there he was going to practice. I was pretty shocked. So I said 'allez Seb!' and I also said "nice haircut!" because he just had his manes chopped off. He smiled and said thanks I guess. Then later that day I ran into him again (by way of stalking him of course) and I asked for an autograph but my pen didn't work so he was actually about to go into the players lounge to get another one when the pen started to write and he dropped his sweater and I picked it up and held it for a good 10 seconds and I said "merci" about 100 times :P As you can assume I was quite starstruck, ha ha!
I talked to his coach Thierry Tulasne last year at a tournament and he was really cool, much more spontanious than dear Seb. But I love'm anyway.