A state of sketch that occurs when a person displays iffy behavior, either because (s)he is just a mess or because (s)he is under or has been under the influence or drugs and/or alcohol, then forgets said dubious behavior altogether. (S)he will probably then use this forgetfulness to excuse further bad behavior that is a result of the initial iffiness (sketch).
Damn, dude, I'm sorry I slept with your girlfriend. I had a crazy night out and my sketchzeimers must've kicked in. It happens when I don't take my meds.
Geez, bro, what's up with you? You asked me to change the date of the photo shoot to accommodate YOUR schedule and when I remind you of it, you have no clue what I'm talking about. You have a serious case of sketchzeimers,
n. an estimate of how 'sketchy' or questionable something is.
v. to estimate how 'sketchy' or questionable something is.
undersketchtimate- to underestimate the level of 'sketchiness'
Bob- Nah man, that dude is straight.
Joe- Are you serious, bro? That guy is like 45 years old, has the scraggliest beard, and is clearly a meth dealer. You have the worsttendency to undersketchtimate.