The strange thing with rhythm is you can think your really tight and have a good sense of it, when actually you can be alittle sloppy. Not sloppy to where you don't get the rhythm right, but your timing on each note can waver alittle bit. This is because your mind has it's own sense of rhythm like when you count, and no one counts 1, 2, 3... at exactly the same time. When your playing with other people, everybody has to count at the same time. I'm pretty sure you understand what I'm saying. The reason why they might say you have bad rhythm is because you may have a hard time playing along with another persons rhythm (counting thing), but your really good with your own rhythm sense. You might be dislocating yourself from the band (not knowing it) by playing to your own rhythm and not the bands. The most common mistake in amatuer bands. The #1 thing to concern yourself with in a band is to listen to each other and play the rhythm at the same time. In a band, the drummer is always the guy who keeps the time. So if he/she says your off, your off and you should remedy this. The best way to get better at rhythm is to always play along with a metronome or drum machine when you practice. Simply because your learn to play along with a time that's not in your head. It will also sharpen the rhythm in your head.

I know I don't take criticism very well either (probably my biggest fault) but you shouldn't let your own ego lead you to be blind to it. Take it and work on it, it's worth it dewd. :)