Over 80 pitches (some with the same folks), over the past 2 years. Here are the warning signs I learned:

• If the VC doesn't ask you how much money you are looking for in the first meeting, they are fishing.
• If the VC doesn't ask how you are going to spend the money, they will not invest.
• If the VC doesn't ask you how much money you have already raised, from whom, how, etc., they are not interested. Just fishing.
• If the VC makes a commitment, say to bring up the deal at the Monday Partner meeting and then get back to you, and they don't, they will not invest. Don't ever, ever call them back. Let it go.
• If the VC doesn't ask who else you are talking to, yet indicates that they only participate in rounds (as opposed to leading them), beware.
• If you get a call from a VC analyst, saying "we just learned about you through...and think you fit well with our firm...would like to schedule an investor presentation..." This will go nowhere. The analyst is boning up on info, and they will suck your brain dry. They have no intentions of investing.
• If they say they are early stage, quickly schedule the meeting, and then indicate that you are "too early...come back when you have...". They have no intentions of investing.
• If the first thing they say when you show up for the meeting is "I know we have an hour setup, but I have an urgent call in 30 minutes..." beware. This is a ploy. Their assistant will come in at the 20 or 30 minute mark and pass along a note to the partner. It looks like a message. The note says "do you want me to kick them out."
• If they spend too much time speaking about themselves, their background, their portfolio, and not enough time getting to know you and your venture, beware.
• If they begin to offer you advice, before you have even finished your thoughts, beware.
• If you can't get to a yes or no quickly, beware.
• If they cancel your meeting a few hours or the night before you are to show up, stating that they will reschedule, beware (note: things come up, but their time is less valuable than yours.)
• If they ask no questions during the meeting, but then want more meetings, beware.
• If they critique the PowerPoint, and offer tons of suggestions for the flow, content, etc. beware.
• If they quickly want to introduce you to others, before they indicate if they are in, beware. This is the infamous punt of death, and they are too chicken shit to say no. No solid VC would want others to participate in a deal they want to be in (if they can cover the round).
• If they drive the process, and make you do all the work without them investing any reciprocating time, beware (don't go off doing a bunch of "research" or homework they ask for simply to email them your findings; ask them "what will this get me...how will you use this to determine if you will make an investment in us...I will walk you though the findings, in person!")
• Beware the investor who claims to be an active angel, but hasn't done a deal in 5+ years.
• Beware the VC who is remaking himself, in realtime, based on your inputs.
• Beware the VC who leads with dogma, like "I never make investments in..." or "I only do...." I have found exceptions to these statements, brought it to their attention, only to hear "well...they made a pivot post funding".
• Ask them this question: "why should I work with you?" and see how they respond. If they offer "strategy" "active board engagement" "operational expertise" "domain expertise", follow up with "what advice would you offer me now...lets imagine you already invested" See where that conversation goes. If it doesn't feel right, move on.
• My last entry, in case you sense things aren't going well: When a VC responds, "Interesting idea; just not something we'd invest in," what does that mean?

I will come up with more thoughts. Great question.