if i want to use IMDb as a guideline and say has an average of 4.9/10 or lower...
-Showgirls (1995) - 4.6/10 average rating. it's amongst My Favorite Movies in general. i give it a 7/10.
but the best of the rest (movies i score a 6/10) within the 4.9/10 or lower average standard...
-The Lost Empire (1984) - 4.9/10 average. but only has 521 votes.
-Striptease (1996) - 4.3/10 average.
-Seed of Chucky (2004) - 4.9/10 average.
-Hardbodies (1984) - 4.8/10 average with only 2,325 votes.
but i guess if you want me to pick a movie that's got a low rating and is probably in that 'so bad, it's good' category i would go with The Lost Empire as i can easily see how many people won't like it (or consider it a 'bad movie') but it worked for me overall.
p.s. IMDb says i have seen 70 titles with a 4.9/10 or lower average rating and the movies i listed above are the only ones i give a thumbs up.
side note: if you let me include 5.4/10 and lower for the average on IMDb there is one more movie that's amongst my favorite movies in general which is Spring Breakers (2012-2013). i give it a 7/10.