I know you're just being memey but...
He had a big ego. When he was criticized for not attacking he got offended instead of taking other people's opinions into consideration. He didn't want civilians weighing in on the situation because he didn't believe they were qualified. The president, being a civilian, was at times ignored for this reason. (It should also be noted that Lincoln kinda let him get away with this shit for a while)
His intel wasn't all that great and he often thought he was outnumbered when he wasn't. His scouts counted the CSA's troops by the number of regimental flags they saw and it was assumed those regiments had the maximum number of troops they could have. In reality they almost never did. The CSA also resorted to trickery to convince the union there were more of them than there really were.
Though, McClellan probably should have known there weren't enough people in the south to form some of the estimates they were coming up with.
To give him due credit, he was extremely good at training, building confidence in his soldiers, and organization. However, the pressure on him was great. If he fucked up it could mean the end of the Union, something he obviously cared about enough to die for. He took his time planning and avoided conflict because, again, he wrongly thought he was out numbered and didn't want to lose troops in any unnecessary engagements because they would be needed later.
He definitely had his strengths and I think he would have performed better were he under the command of another general, one who would pistol whip his ass whenever he got too sassy or slow.