The Uncanny X-Men, Vol. 1

The X-Men are practicing and training when the Professor detects another mutant. They scramble to get ready, knowing that the first to suit up gets to escort Jean Grey, whom they all have romantic interest in (including Professor X!) They track the mutant down at a carnival, where he works as the unmovable Blob. Similarly moved by Jean's appearance, he follows them back to headquarters but turns down their offer to join them. Realizing that he's aware of their secrets, the X-Men try to contain him long enough for the Professor to wipe out his memories, but they fail to do so. The Blob returns with his circus cronies in a pre-emptive strike. The X-Men are overwhelmed by numbers, but slow down the attack long enough for the professor to finish and use his mental intensifier, and wipe out the memories of the entire group simultaneously.