Two tries from centre Eoin O'Malley and a try apiece for Rob Kearney and Gordon D'Arcy secured a bonus point before the interval for the hosts and Isaac Boss completed the rout late on with a solitary Henry Pyrgos try all to show for Lineen's side.
He said: "We got well and truly spanked in that first-half, there was only one team in it.
"They won the contact battle hands down in attack and defence. We made it far too easy for them, it was a walk in the park and the game was over.
"They were a lot more intense than us, very direct and very abrasive. In four or five instances they stripped the ball from us like candy from a baby. It was men against boys.
"We knew it was going to be tough on the Heineken Cup winners' doorstep but we didn't do the simple stuff. That first 40 minutes was tough to watch."
After starting their European campaign with an impressive 26-21 victory over Bath last Sunday, Lineen was particularly disheartened by the result at the RDS Arena and he wants a reaction against Ulster in the RaboDirect PRO12 on Friday night.
He added: "I'm disappointed for the players because they've put a lot of effort in. We couldn't get any momentum and some of the tries were ridiculously easy. If you don't front up, you'll get punished and we did.
"We didn't back up our performance against Bath and we have to fix it for Ulster at home next week. We're under no illusions. We've got to re-group. This is a massive learning curve for the guys."
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