The Collaborative International Dictionary of English v.0.48:

blotto \blot"to\ adj. (bl[o^]t"t[-o])
   drunk[1]. [colloq.]
   [PJC]

WordNet (r) 3.0 (2006):

blotto
    adj 1: very drunk [syn: besotted, blind drunk, blotto,
           crocked, cockeyed, fuddled, loaded, pie-eyed,
           pissed, pixilated, plastered, slopped, sloshed,
           smashed, soaked, soused, sozzled, squiffy,
           stiff, tight, wet]