Well I don't know if tacky is the word I'd use but my least favorites are "Where the Wild Things Are" for Buffy and "She" for Angel.
"WTWTA" is always one I kinda wanna skip. It has its moments but the Buffy/Riley sexathon isn't much fun to watch and actually gets really annoying, and the over sexualised frat party is pretty lame too.
The female circumcision innuendo in "She" is just a little too blatant for me. I don't find it offensive or anything, just a little off-putting. And overall the episode kinda bores me.