This is often a deeply misunderstood passage and it is more than questionable that this passage deals with 'communion' as it is currently undertaken; that is to say the doling out of a wafer, cracker, or piece of bread and a sip or dipping of either wine or grape juice:
For in eating every one taketh before other his own supper: and one is hungry, and another is drunken. - v.21
The picture we have is one of a proper meal (like Passover) not a sacramental ritual. Hence the observation that some eat first while others are left hungry and that some get drunk as well as the tongue in cheek exhortation to eat and get drunk in one's own home:
What? have ye not houses to eat and to drink in? or despise ye the church of God, and shame them that have not? What shall I say to you? shall I praise you in this? I praise you not. - v.22
Indeed the reference made by Paul in verses 23-25 is to the last supper prior to Jesus' death and that was most definitively a meal and not a smidgen of bread:
Now the first day of the feast of unleavened bread the disciples came to Jesus, saying unto him, Where wilt thou that we prepare for thee to eat the passover? And he said, Go into the city to such a man, and say unto him, The Master saith, My time is at hand; I will keep the passover at thy house with my disciples. And the disciples did as Jesus had appointed them; and they made ready the passover. Now when the even was come, he sat down with the twelve. And as they did eat, he said, Verily I say unto you, that one of you shall betray me. - Matthew 26:17-21
Since the specific act of Jesus breaking bread and sharing wine during the meal is referenced as being done for the body (the church) and as a remembrance and proclamation of His death and coming again:
And when he had given thanks, he brake it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me. After the same manner also he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do ye, as oft as ye drink it, in remembrance of me. For as often as ye eat this bread, and drink this cup, ye do shew the Lord's death till he come. - v. 24-26
The overarching context of eating and drinking in an unworthy manner has less to do, then, with participating without searching and repenting personal sins and much more to do with participating in disregard of everyone else in the body of Christ:
Wherefore whosoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord. But let a man examine himself, and so let him eat of that bread, and drink of that cup. For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body. - v.27-29
Some translations (like KJV) have 'the Lord's body" here and others (like NASB) have just "body". The distinction between 'the Lord's body' at the end of v. 29 and 'guilty of the body and blood of the Lord' at the end of v. 27 is given in the entire context and summarized at the closing of the passage:
Wherefore, my brethren, when ye come together to eat, tarry one for another. And if any man hunger, let him eat at home; that ye come not together unto condemnation. And the rest will I set in order when I come. - v.33-34
The incorrect behavior being rebuked in this passage and the resultant condemnation for improper participation have to do with self-serving rather than regard for others within the context of a meal which is supposed to be a remembrance of what Jesus has done for them. Jesus laid down his life for others and they are, figuratively, gobbling Him up at the expense of others.
This isn't so much unforgivable as it is revelatory. They are, perhaps, not behaving as a part of the body because they are not. They are sick and dying (v.30) because they have no vital connection to the vine. They are tares amongst wheat and have not committed an unforgivable sin but, rather, have yet to be forgiven at all:
For first of all, when ye come together in the church, I hear that there be divisions among you; and I partly believe it. For there must be also heresies among you, that they which are approved may be made manifest among you. - v.18-19
There is application to be made in how various churches come together but not just the one aspect of 'communion'. In this, let every one examine themselves ... have I been made a part of the body of Christ or do I serve myself when we come together?