The best is giving and receiving at the same time. Nothing like feeling her quivering thighs and hearing her muffled moans (that just feels damn good too!). The self consciousness normally goes away in that position as they are concentrating on giving you good head. If you get her to that state, don't stick with just lickin teh clit... Go on, live a little - suck on it, tongue the inside, nibble on the perineum, even give that ass a little tip if you're feelin frisky. If she doesn't slap the hell out of you, I swear you'll get the best BJ you have ever had or will ever have. Sometimes even 2 or 3 in a row!
