How long had he known the client? I wouldn’t get too friendly on the first day, but I’m on friendly terms with quite a few clients. Went to a concert 300 miles away with one, dated two others at various points.

I personally don’t use the term “dude”, but it’s not horribly offensive either — one of the aforementioned people used that term quite a bit. Professional distance is great, but you spend 1/3 of your waking life at work, so you’re bound to meet interesting people.