to be slired is to be tired and lazy, most importantly lazy. a person could claim that they are too slired to go play basketball if they are laying on a comfortable couch watching tv, even if they would like to play. it mostly just means that a person is comfortable and unwilling to move.
sam: lets go to albertsons double: im too slired
max: yeah, we're slired
sam: come on you lazy bastards double and max: but we're sliiiiiiired
sam: fuck you guys, im leaving