"The first 40 minutes were close to the most embarrassing 40 minutes I've been involved in," said Gaffney, who drew little comfort from seeing Francisco Leonelli record a second hat-trick in as many home Premiership games.
Gaffney added: "We had a heart-to-heart at half-time, the players realised they had to go out and do something in the second half and they fought a lot harder."
And Gaffney warned his side that they cannot afford a repeat of the slack defending that allowed Wasps to run riot when they face Munster in next weekend's European Cup semi-final.
"If we go through that exercise in conceding tries again next week, the team that punish sides the most is the side we're playing next week," he said.
"They punish sides more than anybody I've seen. We've got to make them play and earn the points they score, not us concede them."
For Wasps, the victory rounded off their eighth straight win and third in a week that has yielded 14 points to take them third in the table. They now have three games remaining - against Gloucester, Newcastle and Leeds Carnegie - to seal their place in the semi-finals.
Director of rugby Ian McGeechan said: "It was a great position to get into by half-time and it was always going to tell a bit in the second half.
"All the time we've looked at fourth place to see how close we were and what we had to do to make sure we were around fourth coming into this last month of the season.
"With three games to go I think it'll go down to last weekend.
"It's in our hands and the players know that but they've got another three games in six days to come and that's a big ask but we've tried to freshen it up and we'll do that again in the last week."