Dunno if you want to target this to only guys eating out girls, but I'll put in my two cents I suppose..
I dated a girl back when I was in high school, so this was like... 5 years ago, but my girlfriend's taste tended to change a little, depending. I wouldn't say it was gooey though. Kinda... salty maybe? I dunno, because it's been awhile. Gooey's also not really a taste, more of a texture, and I think some textures really bother people when they go to eat something. Maybe the consistency seriously bothers him, in the same way I will never be able to swallow jello. The texture gets me every time.
I digress, can't say I liked how my girlfriend tasted, but I didn't think it was horrible. If you think about it, vaginal discharge changes depending on the time of the month, health, and sexual stimulation, so the various kinds of discharge probably taste different. If you feel really strongly about it, ask him why he was willing to try it with multiple girls before you, but not you yourself?