How do you tell a friend that

he is incredibly clueless and crass sometimes?

He's like my second best friend, and he is often completely tactless at times that it's embarassing.

There are some things I like to do which might be considered a little lower on the social scale or very "fannish" at times, and he's come with me to some of these events and made fun of some of the other people there, possibly loud enough for others to hear him. Frankly, it's embarassing.

For instance, I went last July (?) to the midnight book sale when HP6 came out. He was curious, so he asked if he could come. Once there, all he did was make fun of people at the bookstore.

Last week, I wanted to go to Bingo, something I hadn't done in ages, and asked him to come along. When there, all he did was make fun of people, including about their age (many older people there), their often funny habits in playing, etc.

He can be a really nice guy, but I've gotten to the point where asking him to come with me on some of my activities is a quiet conflict on whether I need or want the company more than I would feel embarassed by his comments.

He's a relatively intelligent guy, but I just think he needs a class in sensitivity when it comes to some things. It's a bit of a gamble in whether he will behave himself or not in front of others.

If he's really a good friend, you should be able to do that. Hang on, have to take a call at work./

and don't invite him to affairs that he sounds prone to do. It reads as though that by now you can predict which types of activities he is likely to mock others, out loud.