Ask about how the investor has worked with other companies. Just because you don't have a previous relationship with someone is no reason not to work with them now. If the investor is a jerk, be courteous but follow your instincts. Don't be worried that this is the only investor out there. Successful money raising is a process, not an event.
Life is too short to deal with jerks.
If you can't stand him, don't. Even if a jerk decides to invest, just think how painful it is going to be to work with this person as you try to build your company. Selling your deal will probably be one of the first major business challenges you take on as an entrepreneur. Don't go into this battle unprepared. Create a well-developed business plan, a snappy elevator pitch, and make sure you've done research on your audience.