1. This is a lame joke.
- this is a bad joke. it's not funny or its been told so many times that people are bored of it.
2. Lame guys.
- this can mean many different negative things all kind of meaning 'not cool'
Lame guys could be:
-boring
-rude or mean
-lazy or unmotivated
-unsuccessful
-not romantic enough
-annoying
... the list could go on forever.