tl;dr can be used to poke fun at a post which is well thought out and informative, but flippin long...see 'Pokey' in the small stakes NL sticky.... I.e. It's just a joke...
Usually it's just a gentle wisecrack, I'd guess when people post masses of hh's in BBV about how good/bad they run, it's more pointed. i'e. No one cares
[Edit] Even if you know exactly what tl;dr means....still look at Pokeys stuff in the sticky, man's an artist.