"I have went"
If the pedants will look away long enough for me to say "It's not very irregular.", then I will. (If they won't, then would the rest of you be so good as to skip the rest of this post. Otherwise we'll get logical paradoxes.)
I think "went" is to "wend" what "spent" is to "spend" and so "I have went" is about as irregular as "I have spent" and therefore rather more regular than "I have gone". It should, of course, be "I have goed" but I imagine it is too late to insist on that now.
Quite how the verbs to go and to wend (as in, "wend their merry way back from the pub") ever became entangled remains as mysterious as ever, of course, but most western European languages seem to have one or two stupendously irregular verbs with different persons and tenses taken from different root verbs in older languages. I think it is some kind of competition.