I think the one that comes to mind for me more than any other is when Rocky is peddling the streets in Rocky V. I thought, 'WTF! Hollywood has hit a new low!' And I have to put on my shades to disguise my embarrassment for having seen it.
When Kelly McGillis turned up as the flight instructor in "Top Gun". I don't know why, but I laughed out loud when that scene came on. Maybe because it just seemed so contrived and... "Hollywood". Untrue to anything that would happen in real life, even in this already goofy film....
All of those 1950s and early '60s Westerns where the men all had short, 1950s haircuts and no facial hair. Plus those "frontier women" with Kay Starr (as opposed to Belle Starr) hairstyles and crunchy bouffants. lol Takes me out of the movie every time.
My favorite BLAM moment in a film is Don Cheadle's maddeningly bizarre line "You two look like a pair of seals fighting over a grape" in Iron Man 2 when he witnesses Robert Downey, Jr. and Gwyneth Paltrow making out on a rooftop.