"Bear with me . . ."

Why do we use this phrase . . . really? It's just soliciting pity for yourself, and nobody wants to be accused of that. If you're in a less than preferable position of preparedness (or mental state - anything really) doesn't matter. Just accept the facts and move on, with out dragging your poor audience on a major guilt trip for  your blasted inadequacies. 

Understandably, there are a few occasions (so few that I can't even think of an example) where this is appropriate, but those are indeed few, so maybe just avoid the attempts at garnering forced sympathy from your audience. All you need to do is smile, think fast, and move on.